FMSLogo Code

Add missing #include to fix a build break when compiling w/o precompiled headers

Fix the File API's special "clipboard" file to correctly handle Unicode.
It now writes a BOM and encodes the fake file in UTF-8.

Fix a bug that corrupted some three-byte UTF-8 character encodings

Merge in changes to clipboard handling from trunk.

Merge in changes to clipboard handling code from trunk.
The merged logic is not correct for Unicode, because it doesn't insert a BOM to the beginning of the clipboard file.
This will be fixed in a subsequent commit.

Replace win32-specific clipboard code in the File API with platform-independent code.
This brings FMSLogo one step closer to running on GNU/Linux.
It also fixes a bug where a NUL character was written to the end of the clipboard file.

Fix a bug in the logic for 3-byte encodings of UTF-8.

Declare write_char_utf8 as "static", since it's not used outside this file.

Include debugheap.h to fix crashes when FMSLogo is built in debug mode without precompiled headers.

Extend DLLCALL to support passing PWSTR strings with 'U'
This enables Logo programs to call many more system functions.