autogen.sh: Honor NOCONFIGURE=1

This is adapted from telepathy-logger's autogen.sh.  See
http://people.gnome.org/~walters/docs/build-api.txt
for rationale behind NOCONFIGURE=1.
build: Add ‘-I m4’ to ACLOCAL_AMFLAGS

This shuts up an automake warning and ensures that in-tree m4 macros are found
by aclocal.

https://bugs.freedesktop.org/show_bug.cgi?id=70965
build: Add AM_PROG_AR to configure.ac

This shuts up an automake warning about needing it when using a non-POSIX
archiver.

https://bugs.freedesktop.org/show_bug.cgi?id=70965
build: Update configure.ac according to autoupdate

https://bugs.freedesktop.org/show_bug.cgi?id=70965
build: Add GUPnP libraries to Libs.private in pkg-config file

They’re private dependencies which are needed on the linker command line when
linking statically against libnice.

https://bugs.freedesktop.org/show_bug.cgi?id=70965
Silence aclocal warning by changing the order of the macros
Add special case to make it compile on Solaris
agent: Getting the local candidates returns a copy, fix the doc
agent: Add API to retrieve the selected GSocket

This should be used only when the protocol has it's own keepalive mechanism
agent: Clarify valid range of stream and component IDs

Valid IDs will never be 0, which is convenient.
build: Update AC_CONFIG_HEADERS instead of AC_CONFIG_HEADER

The latter is deprecated.
build: Delete ar-lib in maintainer-clean build target
build: Update .gitignore file
Fix variable shadowing
examples: Remove redundant non-NULL checks

The return value of g_strsplit() can never be NULL.
Add missing ‘default’ cases to switches

This shuts GCC’s -Wswitch-default warning, and makes the code flow a
little more explicit.

This introduces no functional changes.
Fix strict aliasing of sockaddr structures

Casting from one struct sockaddr type to another breaks C’s strict
aliasing rules (variables of different types cannot alias). Fix this
cleanly by using unions of struct sockaddrs to convert between the
types (i.e. type-punning).

I wish sockaddr didn’t have to be this painful.

See:
http://gcc.gnu.org/onlinedocs/gcc-4.4.1/gcc/Optimize-Options.html#Type_002dpunning
agent: Add printf function attribute

This shuts a compiler warning up and allows for format string checking
of debug messages. (See future commits for the fixes this has resulted
in.)
agent: Add missing format specifiers to debug messages
agent: Fix format specifiers in debug messages

Mostly problems with the specifier for gsize.