Remove TYPE_* constant macros and use object_type enums consistently.

Remove TYPE_* constant macros and use object_type enums consistently.

This updates the type-enumeration constants introduced to reduce
the memory footprint of "struct object" to match the type bits
already used in the packfile format, by removing the former
(i.e. TYPE_* constant macros) and using the latter (i.e. enum
object_type) throughout the code for consistency.

Eventually we can stop passing around the "type strings"
entirely, and this will help - no confusion about two different
integer enumeration.

Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>