Show library version in configure.
Fix configure under OS X Yosemite.
Revert overzealous use of %s in printf

The error and warning in configure contains backslashes, and these need
to be interpreted.  Therefore, they must be embedded directly in the
format strings.
Minor cosmetic fix
Merge branch 'master' into 2.5.0-release
Bump the version number.
Quieter building of doc files under OS X.