* configure.in: add a --with-default-emulation argument (part of #115750).  Use
	AS_HELP_STRING wherever we need help strings.
* vte.pc.in, vte-uninstalled.pc.in: add DefaultEmulation variable
* vte.spec: specify "xterm" as the default-emulation, even though it's the
	default default
* termcaps/Makefile.am: build and install the default emulation's
	termcap, assuming it's some kind of xterm variant.
* src/keymap.c(_vte_keymap_map): check for xterm-xfree86 definitions
	if the terminal type includes xterm, not if it exactly matches xterm
* src/reaper.c(vte_reaper_add_child): add.  The glib 2.4 SIGCHLD watcher
	requires us to register particular PIDs for monitoring, so now we
	require applications to do so.
* src/reaper.c(vte_reaper_child_watch_cb): add.
* src/reaper.c(vte_reaper_init): Don't hook the SIGCHLD handler if we're
	running under glib 2.4, expect to use the g_child_watch mechanism.
* src/vte.c: remove hard-coded definition of VTE_DEFAULT_EMULATION, to be
	picked up from config.h instead.
* src/vte.c(vte_sequence_handler_cs): remove stray debug printfs.
* src/vte.c(vte_terminal_insert_char): only do what we were doing for xn if LP
	was also set (#141445).
* src/vte.c(vte_terminal_get_default_emulation): add.
* src/vte.c(_vte_terminal_fork_basic): call vte_reaper_add_child for new
	children.