Cleanup up non-prototyped functions (static) and const-correctness

More fixes based on the compiler directives -Wcast-qual -Wwrite-strings
-Wmissing-prototypes -Wmissing-declarations. Not everything with regards
to -Wcast-qual has been fixed as some have unwanted consequences for the
rest of the code.
diff --git a/library/md_wrap.c b/library/md_wrap.c
index 5f64df7..f98550f 100644
--- a/library/md_wrap.c
+++ b/library/md_wrap.c
@@ -5,7 +5,7 @@
  *
  * \author Adriaan de Jong <dejong@fox-it.com>
  *
- *  Copyright (C) 2006-2010, Brainspark B.V.
+ *  Copyright (C) 2006-2013, Brainspark B.V.
  *
  *  This file is part of PolarSSL (http://www.polarssl.org)
  *  Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
@@ -76,7 +76,7 @@
     md2_finish( (md2_context *) ctx, output );
 }
 
-int md2_file_wrap( const char *path, unsigned char *output )
+static int md2_file_wrap( const char *path, unsigned char *output )
 {
 #if defined(POLARSSL_FS_IO)
     return md2_file( path, output );
@@ -246,7 +246,7 @@
     md5_finish( (md5_context *) ctx, output );
 }
 
-int md5_file_wrap( const char *path, unsigned char *output )
+static int md5_file_wrap( const char *path, unsigned char *output )
 {
 #if defined(POLARSSL_FS_IO)
     return md5_file( path, output );