Fixes for malloc / calloc + other fixes

This patch contains:

* checks for malloc return value + treat callers;
* modified malloc() + ZeroMemory() to calloc();
* misc fixes of micro errors seen during the code audit:
** some invalid checks in gcc.c, also there were some possible
integer overflow. This is interesting because at the end the data are parsed
and freed directly, so it's a vulnerability in some kind of dead code (at least
useless);
** fixed usage of GetComputerNameExA with just one call, when 2 were used
in misc places. According to MSDN GetComputerNameA() is supposed to return
an error when called with NULL;
** there were a bug in the command line parsing of shadow;
** in freerdp_dynamic_channel_collection_add() the size of array was multiplied
by 4 instead of 2 on resize

rdtk/sample/rdtk_x11.c

@@ -95,9 +95,13 @@ int main(int argc, char** argv)
 	XFree(pfs);
 
 	engine = rdtk_engine_new();
+	if (!engine)
+		return 1;
 
 	scanline = width * 4;
 	buffer = (BYTE*) malloc(scanline * height);
+	if (!buffer)
+		return 1;
 
 	surface = rdtk_surface_new(engine, buffer, width, height, scanline);