Failing to do on clients was causing TLS 1.3 negotiation to fail.

Fixes bug 28245; bugfix on 0.2.9.15, when we added TLS 1.3 support.

Related to fix for 28202.

Remember, you can't check to see if there are N bytes left in a
buffer by doing (buf + N < end), since the buf + N computation might
take you off the end of the buffer and result in undefined behavior.

Fixes 28202; bugfix on 0.2.0.3-alpha.

Treat backtrace test failures as expected on NetBSD, OpenBSD, and
macOS/Darwin, until we solve bug 17808.

(FreeBSD failures have been treated as expected since 18204 in 0.2.8.)

Fixes bug 27948; bugfix on 0.2.5.2-alpha.

Use the Travis Homebrew addon to install packages on macOS. The package
list is the same, but the Homebrew addon does not do a `brew update` by
default.

This makes builds faster, at the cost of using slightly older packages.

Implements ticket 27738.

On GCC and Clang, there's a feature to warn you about bad
conditionals like "if (a = b)", which should be "if (a == b)".
However, they don't warn you if there are extra parentheses around
"a = b".

Unfortunately, the tor_assert() macro and all of its kin have been
passing their inputs through stuff like PREDICT_UNLIKELY(expr) or
PREDICT_UNLIKELY(!(expr)), both of which expand to stuff with more
parentheses around "expr", thus suppressing these warnings.

To fix this, this patch introduces new macros that do not wrap
expr.  They're only used when GCC or Clang is enabled (both define
__GNUC__), since they require GCC's "({statement expression})"
syntax extension.  They're only used when we're building the
unit-test variant of the object files, since they suppress the
branch-prediction hints.

I've confirmed that tor_assert(), tor_assert_nonfatal(),
tor_assert_nonfatal_once(), BUG(), and IF_BUG_ONCE() all now give
compiler warnings when their argument is an assignment expression.

Fixes bug 27709.

Bugfix on 0.0.6, where we first introduced the "tor_assert()" macro.

The spec only allows the characters [A-Za-z0-9-].

Fix on b2b2e1c7.
Fixes #27316; bugfix on 0.2.9.4-alpha.

It's possible for a unit test to report success via its pipe, but to
fail as it tries to clean up and exit.  Notably, this happens on a
leak sanitizer failure.

Fixes bug 27658; bugfix on 0.2.2.4-alpha when tinytest was
introduced.

Fixes bug 27344, where we'd break compatibility with old tors by
rejecting RSA1024 and DH1024.

It is not supported, and always fails. Some compilers warn about the
function pointer cast on 64-bit Windows.

Fixes bug 27461; bugfix on 0.2.2.23-alpha.

gcc 8 warns that extend_info_t.nickname might be truncated by strncpy().

But it doesn't know that nickname can either contain a hex id, or a
nicknames. hex ids are only used for general and HSDir circuits.

Fixes bug 27463; bugfix on 0.1.1.2-alpha.

GetProcAddress() returns FARPROC, which is (long long int(*)()) on
64-bit Windows:
https://msdn.microsoft.com/en-us/library/windows/desktop/ms683212(v=vs.85).aspx

But GetAdaptersAddresses() is (long unsigned int(*)()), on both 32-bit
and 64-bit Windows:
https://docs.microsoft.com/en-us/windows/desktop/api/iphlpapi/nf-iphlpapi-getadaptersaddresses

So gcc 8 issues a spurious "incompatible function pointer" warning
about the cast to GetAdaptersAddresses_fn_t.

Silence this warning by casting to a void function pointer, before
the cast to GetAdaptersAddresses_fn_t.

This issue is already fixed by 26481 in 0.3.5 and later, by removing
the lookup and cast.

Fixes bug 27465; bugfix on 0.2.3.11-alpha.

When we use echo in Travis, don't pass a --flag as the first argument.

Fixes bug 27418; bugfix on 0.3.4.7-rc.

When a Travis build fails, and showing a log fails, keep trying to
show the other logs.

Fixes bug 27453; bugfix on 0.3.4.7-rc.

Before running make test-network-all, delete old logs and test result
files, to avoid spurious failures.

Fixes bug 27295; bugfix on 0.2.7.3-rc.

Part of 27295.

test.c no longer uses lround(), so we don't need to declare it,
and we can use math.h for fabs().

Fixes bug 27185; bugfix on 0.2.2.2-alpha.

It's redundant, because all the non-default builds use gcc on Linux.

Part of 27252.

Part of 27252.

Part of 27252.

Part of #27252.