Added Aragonese translation
glib/tests/mappedfile: Copy test file before writing to it

This way we're *always* testing writability rather than only sometimes
doing it in the source directory.

https://bugzilla.gnome.org/show_bug.cgi?id=699079
glib/tests: Use explicit file listings

This is a preparatory commit for installed tests work; having things
cleanly categorized helps.

https://bugzilla.gnome.org/show_bug.cgi?id=699079
glib/tests: Drop unnecessary SRCDIR definitions

It's always going to be defined, we don't support compiling these
tests "by hand".  This is a cleanup commit for the installed tests
work.

https://bugzilla.gnome.org/show_bug.cgi?id=699079
Add --enable-installed-tests configure option

See https://live.gnome.org/GnomeGoals/InstalledTests for more
information.

The tests now support being run both uninstalled and installed, so
'make check' works for those who want it.  For tests which need data
files, the way this works is they look in the compiled in value of
SRCDIR by default, and the generated tests use "env G_TEST_DATA=" to
override that.

This patch only converts glib/tests for now; if this patch looks good,
I'll do the rest of the tests.

https://bugzilla.gnome.org/show_bug.cgi?id=699079
Moved the G_MAIN_POLL_DEBUG stuff to gmain-internal.h

Now that code is about to drift from gmain.c into the poll backend,
the debug infrastructure should better be shared in the header.
I'm too lazy to deduplicate it in gpoll.c, though.
Factored the poll backend out of GMainContext

Defined GMainContextFuncs, the backend vtable for
pluggable main loop implementations.
The new constructor g_main_context_new_custom() can be used
to create contexts with custom backends (and is used internally
for built-in backends).

This first backend, made largely from the existing code, is special
in another way: the methods of GMainContext that were designed around
GPollFunc will be only supported by the poll backend.
The context will switch to the poll backend to complete
any of these functions.
Added the epoll backend for GMainContext

The new backend necessitates other changes:
Now that adding and removing descriptors to the poll may
produce failures, some of which are benign, it's important to
handle the failures when blocking and unblocking sources for recursion,
so that we don't end up in a more serious error when e.g. unblocking
a source that has had its descriptor closed and then
"temporarily" removed from the poll for dispatch.
Erased the run/quit functions from GMainContextFuncs

These are a dead API: any existing or planned backend supports
single-step iteration. They introduce functionality regressions.
They needed to go, but I prefer to leave them in the history
for reference.
Make use of the epoll backend, with a runtime fallback to poll

Falling back to poll is done in two cases:
1. At construction, if epoll_create fails.
2. When the client calls g_main_context_set_poll_func().