fast-import: make code "-Wpointer-arith" clean
fast-import: make code "-Wpointer-arith" clean

The dereference() function to peel a tree-ish and find the underlying
tree expects arithmetic to (void *) to work on byte addresses.  We
should be reading the text of objects through a char * anyway.

Noticed-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>
Signed-off-by: Jonathan Nieder <b57189c5f2fd5b3daf3350a77fde90def1080fa5@gmail.com>

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