Define PERL_NO_GET_CONTEXT in all perl source files

This removes the calls to Perl_get_context() that get automatically
added to XS code for ancient source code compatibility reasons.

The result is about a ~60K size reduction in the binary (based on
comparing two 64-bit stripped irssi binaries compiled
--with-perl-staticlib).

src/perl/common/Channel.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Channel  PACKAGE = Irssi

src/perl/common/Core.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 #include "irssi-version.h"
 #include "core.h"

src/perl/common/Expando.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 #include "expandos.h"
 

src/perl/common/Ignore.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Ignore  PACKAGE = Irssi

src/perl/common/Irssi.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 static int initialized = FALSE;

src/perl/common/Log.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Log  PACKAGE = Irssi

src/perl/common/Masks.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Masks  PACKAGE = Irssi

src/perl/common/Query.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Query  PACKAGE = Irssi

src/perl/common/Rawlog.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Rawlog  PACKAGE = Irssi

src/perl/common/Server.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 
 MODULE = Irssi::Server  PACKAGE = Irssi

src/perl/common/Settings.xs

@@ -1,3 +1,4 @@
+#define PERL_NO_GET_CONTEXT
 #include "module.h"
 #include "misc.h"