changes for 4.4:
- pulled upstream patch to fix bug #27017, #28824 and #28872
- using a workaround to address bug #27299, this was fixed in
development branch 4.5.3 by using a new version of gnulib.
however, upgrading gnulib needs too much effort here.
changes for 4.2:
- 4.2.31's gnulib/m4/extension.m4 won't work with autoconf 2.65,
fix it by removing gnulib's AC_USE_SYSTEM_EXTENSIONS