Simplify search code.

There's no real benefit to avoiding compiling empty regular expressions, and
the code is much simpler if we streamline the codepath.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Simplify callback type checking.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Eliminate useless callback type checks.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>