subvertpy wrapper: check against Subversion version compiled against. The previously used method for checking the Subversion version, subvertpy.wc.version(), reported back the version of the runtime library used. This is not what we're interested in; we want to know what version it was compiled against. These functions were not available in Subvertpy 0.7.3, necessitating the earlier bump of the version requirement to 0.7.4.