Apparently it does a explicit version check for automake, but in such a
way that it needs to be patched on new automake versions. Patch this out
while we await the PR upstream to be merged into master.
See: https://github.com/jstedfast/gmime/pull/180
Build libstemmer as a shared library. Use current mainline since that
at least supports build system args.
Shared lib patch courtesy of Stefano Rivera <stefanor@debian.org>,
updated to current head.
