update to-do list. remove --disable-shared. remove a memory leak. fix a

update to-do list. remove --disable-shared. remove a memory leak. fix a

* README: update to-do list.
* autogen.sh: remove --disable-shared.
* src/pty.c: remove a memory leak.
* src/termcap.c: fix a possible read-before-start-of-buffer.
* src/trie.c: use iconv instead of mbrstowcs, even if it's just ASCII->W_CHAR_T.
* src/vte.c: fix a few memory leaks; only reset the IM context when we're realized, which is the only time we actually have an IM context; don't create a copy of a pixbuf if we don't need to desaturate it, just ref it and use it directly.