CLEANUP: pattern: rename pat_ref_commit() to pat_ref_commit_elt()

CLEANUP: pattern: rename pat_ref_commit() to pat_ref_commit_elt()

It's about the third time I get confused by these functions, half of
which manipulate the reference as a whole and those manipulating only
an entry. For me "pat_ref_commit" means committing the pattern reference,
not just an element, so let's rename it. A number of other ones should
really be renamed before 2.4 gets released :-/