Supress warnings in Glulxe
No need to initialize private struct members to 0

At the beginning of the class init function, the entire private
struct is filled with 0 bytes.
Use init and clear for GMutex and GCond

- g_mutex_init() replaces g_mutex_new()
- g_mutex_clear() replaces g_mutex_free()
- g_cond_init() replaces g_cond_new()
- g_cond_clear() replaces g_cond_free()

The old functions were deprecated and the new functions were added as
of GLib 2.32.

This requires all structures to use GMutex members instead of GMutex *
pointers; likewise for GCond. Since we cannot set the GMutex * pointers
to NULL anymore when the ChimaraGlk widget is finalized, we add an
after_finalize flag that is set at the beginning of
chimara_glk_finalize().
Use g_cond_wait_until() instead of g_cond_timed_wait()

This bumps the GLib version requirement to 2.32; that is also the
version in which g_cond_timed_wait() was deprecated.
Use g_thread_try_new() instead of g_thread_create()

g_thread_create() was deprecated in GLib 2.32. We don't use
g_thread_new() because the program should not abort if the thread
could not be created; rather, it should display an error message
and refuse to start the game.
Use statically-allocated thread private data

Dynamically allocating GPrivate is discouraged, and g_private_new()
is deprecated since GLib 2.32.
Don't use g_thread_init() anymore

g_thread_init() is called automatically when the library loads.
Remove support for older GLib and GTK versions

The iLiad Reader was holding us back to GTK 2.6, but that product
is discontinued and the company is bankrupt.
No need to include empty default signal handlers