This patch fixes problems with the current windows clipboard cut and paste.

*Issues:
- The current cut & paste in the text window has support for both the window's system clipboard and also the internal text buffer.
Control +v/c does internal copy paste from within the textarea
Shift+Control +v/c does win32 copy/paste from the clipboard.
It is not needed to have a separate buffer on windows for the internal textarea and stick the windows clipboard with a non-standard windows shortcut. Control+v/c is the standard cut/paste keys in every known windows application.
- The windows clipboard has a subtile memory allocation error that causes a block of memory to be leaked.

*Resolution
- txt_copy_clipboard/txt_paste_clipboard is called and if there is a system cut/paste available this one is used. When there is not a system cut & paste the internal blender default is used.
- new char* to fix memory leak. Problem was reassignment of the copybuffer pointer causes a leak of the copybuffer memory block.

Notes:
- Tested on windows xp. Works great.