Fix Haiku compat version comparison

Pass REL_EQ instead of "flags" to pool_match_flags_evr when comparing
the compat version, since "flags" points in the same direction as the
compat version relation and the result would therefore always be true.
repo_haiku: Also handle the compat version
repo_haiku: Prepend "pkg:" to package's solvable name

This prevents a package itself being matched against the
"requires" of other packages, unless explicitly specified with the
"pkg:" prefix there as well.
Not sure, if this is a good solution. I didn't find any way to tell
libsolv to ignore the package solvable for this purpose at least.