See the comments in MR!424.
Basically realpath relies on false assumptions (probably ones which used
to be true when the API got created) on the max size of a path. Actually
nowadays paths can be much bigger than what the macro advertizes or can
even be unbounded.
The Linux version of realpath() allows the second parameter to be NULL,
in which case it would allocate the buffer, exactly for this reason
(written in the BUGS section on the man). Unfortunately this behavior is
not standardized in POSIX and the man from Apple I found does not
indicate it will do this.
So let's use g_canonicalize_filename() instead, which seems to do the
right thing. Similarly use g_strdup_printf instead of g_snprintf().
Cherry-picked from commit 6f4fac7715eb66a90727f931246c93cd8e13a819 with
some conflict resolution.
566be5e986