Remove buggy xterm workaround in tui_dispatch_ctrl_char()

Remove buggy xterm workaround in tui_dispatch_ctrl_char()

The function tui_dispatch_ctrl_char() has an old workaround (from 1999)
for buggy terminals and/or ncurses library that don't return page
up/down keys as single characters.  Because the workaround is so old, I
think the bug it is targetting is no longer relevant anymore.

But more importantly, the workaround is itself buggy: it 1) performs a
blocking call to wgetch() and 2) if the key returned by wgetch() does
not make up a relevant key sequence it throws away the input instead of
pushing it back via ungetch().  And indeed the workaround breaks Alt-key
sequences under TERM=xterm because of bug #2.

So this patch removes the buggy workaround and tidies up the function
accordingly.

I personally tested this change on a recent xterm (with TERM=xterm) in
Fedora 20 and had no problems with having ncurses properly interpret
page up/down keys.  And Alt-key sequences now work when TERM=xterm too.

gdb/ChangeLog:

	* tui/tui-command.c: Remove include of <ctype.h>.
	(tui_dispatch_ctrl_char): Remove workaround for xterm terminals.