Lower the minimum required automake version
Lower the minimum required automake version

The minimum required automake version was raised from 1.7 to 1.15 by
commit a6c11d6cd89ac391dfb81bc2b7eb2b9fb31d7da6.  This new requirement
seems to be unnecessarily high, at least, the project builds using
automake 1.14 just fine.

besser82/libxcrypt,besser82/libxcrypt,besser82/libxcrypt,besser82/libxcrypt