ui-tree: unify with ui-view, use path to select tree/blob

This teaches ui-tree to show both trees and blobs, thereby making ui-view
superfluous. At the same time, ui-tree is extended to honour the specified
path instead of requiering a tree/blob sha1.

Makefile

@@ -14,7 +14,7 @@ CGIT_SCRIPT_NAME = cgit.cgi
 
 EXTLIBS = git/libgit.a git/xdiff/lib.a -lz -lcrypto
 OBJECTS = shared.o cache.o parsing.o html.o ui-shared.o ui-repolist.o \
-	ui-summary.o ui-log.o ui-view.o ui-tree.o ui-commit.o ui-diff.o \
+	ui-summary.o ui-log.o ui-tree.o ui-commit.o ui-diff.o \
 	ui-snapshot.o ui-blob.o
 
 CFLAGS += -Wall