In GimpTempBuf, add gimp_temp_buf_lock() and gimp_temp_buf_unlock()
functions, which lock/unlock the buffer for data access. Unlike
gimp_temp_buf_get_data(), which returns a direct pointer to the
buffer's data, the new functions take a format parameter and may
return a temporary buffer, allowing the buffer to be accessed using
an arbitrary format.
Change gimp_pixbuf_create_buffer() to copy the pixels if a linear
buffer cannot be created. Add functions that convert between
GimpTempBuf and GdkPixbuf. Fix users of gimp_pixbuf_create_buffer()
to make the least possible copies. Patch modified by Mitch.
Ell