Update where rc1 tag is and the name of make dist's tarball

The rc1 tag is moved to the 5 so that resulting strings are 2.5rc1
rather than 2.5.0rc1. This makes the naming consistent with previous
PLFS versions.

The name of the generated tarball now uses plfs_VERSION_FULL instead of
coming up with its own name. Now the name of the tarball will be
consistent with all other version strings (ie the version string that
ends up in the library name).
Update spec file and documentation on how to test it.

The spec file can now handle version strings of variable length without
having to change the spec file beyond the version numbers. This means
that it isn't necessary to change what files need to be included when
the version string changes a library name beyond what the rpm syntax can
handle. For example, the spec file can deal with 2.5.1 just as easily as
it deals with 2.5; only the version numbers have to be updated.