xim: one file at the top level, keymaplookup in it

xim/keymap.c held one 37-line function apart from xim.c, with its own
prototype typed by hand in xim.c and nelem spelt out because it avoided
dat.h — all so that a test could link it without imdkit, though the XIM
adapter test #includes xim.c whole anyway.  It lives in xim.c now, and
xim.c, the last file of its directory, sits beside ibus.c.

.gitignore

@@ -11,8 +11,6 @@
 /tests/daemon_collision_test
 /tests/daemon_failure_test
 /tests/daemon_restart_test
-/xim/*.o
-/xim/xim_test
 /gtk/im-strans.so
 /bench/bench
 /bench/perf.data*