autoreconf 2.62 can't handle AS_VAR_IF in our configure.ac

configure.ac:607: error: possibly undefined macro: AS_VAR_IF If this
token and others are legitimate, please use m4_pattern_allow. See the
Autoconf documentation.
autoreconf-2.62: /usr/local/bin/autoconf-2.62 failed with exit status: 1

http://www.winehq.org/pipermail/wine-devel/2010-May/083662.html indicates that autoreconf 2.62 can't handle AS_VAR_IF.

We introduced AS_VAR_IF in two places in git commit 21ac2928 which went into Tor 0.2.5.2-alpha.

If this is easy to fix, it seems wise to do so -- we have some relays (including at least one directory authority) that are still on autoreconf 2.62.

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