Compilation fixes for MSVC

It builds and runs with 32-bit, not quite tested yet
Add a MS visual studio 2010 solution

Note:
 * Only 32-bit version is supported for now.
 * project file for libffi comes from https://github.com/pgregory/libffi-msvc
Do not call OS_Free directly

The core could be built as a library, in which case OS_Free might not
exist.
Fix a typo
Turn off debugging outputs
Move the declaration of As_OS_Str to host-lib.h

To avoid redundence. Ideally, it should be auto-generated, but
make-os-ext only extracts functions starting with "OS_".
Avoid undeclared functions
Scan host-graphics.c for OS_* functions
Declare Crash()
Avoid sign mismatch in comparison
Shutoff compiler warnings with explicit type conversion
Avoid signed integer overflow

"-" on unsigned produces unsigned, and assigning to a signed integer
will cause overflow, which is undefined.
Enable prebuilt.bat
Reduce the executation difference in embedded script

This minimizes the changes needed to embed a script
Avoid signed integer overflow

"-" on unsigned produces unsigned, and assigning to a signed integer
will cause overflow, which is undefined.
Avoid integer overflow
Merge branch 'msvc' into atronix

Conflicts:
	src/core/f-int.c