Switch to using G_DISCARD for call_pv

PUTBACK was being called even for the error path which didn't use the
stack. Emitting the "script error" signal can involve running Perl code
(Irssi:core::destroy) therefore the stack can be reallocated. This
can result in the perl stack being corrupted because the local stack
pointer is out of date (although as it's use of freed memory the crash
is not always instant).
Correct use of perl stack macros

Further to pull #49 this is the result of an audit of the use of perl
stack macros. There were several cases where PUTBACK was being called
where the stack pointer could be out-of-date.

Also some misc. cleanup where the macros were used needlessly.
rename configure.in -> configure.ac

Silences warning on newer autoconf:

aclocal: warning: autoconf input should be named 'configure.ac', not
'configure.in'
add AC_CONFIG_MACRO_DIR([m4]), move *.m4 files to m4/

Silences notice on newer autoconf:

libtoolize: Consider adding `AC_CONFIG_MACRO_DIR([m4])' to configure.ac and
libtoolize: rerunning libtoolize, to keep the correct libtool macros in-tree.

This helps keep the top-level build directory clean, too
s/INCLUDES/AM_CPPFLAGS/g

Silences warnings on recent automake such as:

src/core/Makefile.am:3: warning: 'INCLUDES' is the old name for
'AM_CPPFLAGS' (or '*_CPPFLAGS')
Use PREFIX from 005 to decide if a nick flag is of op level

Fixes #61.
add print_text_after_time to specify time stamp for lines
add signal for line removal from textbuffer
Update crash.txt to point at github