gitweb: There can be more than two levels of subdirectories
gitweb: There can be more than two levels of subdirectories

Earlier code to read .git/refs/{tags,heads} hierarchy had a
hardcoded up-to-two-level assumption.  Lift it by using
File::Find.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git