stdio compat layer for plugins

This is attempt to simplify porting programs to rockbox (as plugins).
Currently this compat layer implements:
fopen(), fclose(), fflush(), fread(), fwrite(), fseek(), fseeko(),
ftell(), ftello(), fgetc(), ungetc(), fputc(), fgets(), clearerr(),
ferror(), feof(), fprintf()

In order to use it you need to include in ported sources
"lib/stdio_compat.h"

Change-Id: I5add615dd19c5af9c767ccbfb1bd5a4e466741cb

apps/plugins/lib/SOURCES

@@ -11,6 +11,7 @@ highscore.c
 simple_viewer.c
 display_text.c
 strncpy.c
+stdio_compat.c
 
 #if defined(HAVE_LCD_BITMAP) && (LCD_DEPTH < 4)
 grey_core.c