initial stub implementation of implicit thread/this

initial stub implementation of implicit thread/this
pointer	argument; builds/tests on Solaris, win32
hasn't been fixed up yet; proto.h, global.sym and
static function decls are now generated from a common
database in proto.pl; some inconsistently named
perl_foo() things are now Perl_foo(), compatibility
#defines provided; perl_foo() (lowercase 'p') reserved
for functions that take an explicit context argument;
next step: generate #define foo(a,b) Perl_foo(aTHX_ a,b)

p4raw-id: //depot/perl@3522