Log Message:
couchdb: Build against lang/erlang21.

This version of couchdb, as well as the current version of couchdb 3.x, is
incompatible with OTP 23.  While here fix hardcoded paths in patch-aa, making
it clear that this package can't be all that popular ;-)

Bump PKGREVISION for good measure even though this package previously could not
build, in case someone still has a version from before lang/erlang was bumped
lying around.