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/ssl_srv.c b/library/ssl_srv.c
index 5625644..61a155c 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -195,9 +195,9 @@
 }
 
 #if defined(POLARSSL_ECP_C)
-int ssl_parse_supported_elliptic_curves( ssl_context *ssl,
-                                         const unsigned char *buf,
-                                         size_t len )
+static int ssl_parse_supported_elliptic_curves( ssl_context *ssl,
+                                                const unsigned char *buf,
+                                                size_t len )
 {
     size_t list_size;
     const unsigned char *p;
@@ -231,9 +231,9 @@
     return( 0 );
 }
 
-int ssl_parse_supported_point_formats( ssl_context *ssl,
-                                       const unsigned char *buf,
-                                       size_t len )
+static int ssl_parse_supported_point_formats( ssl_context *ssl,
+                                              const unsigned char *buf,
+                                              size_t len )
 {
     size_t list_size;
     const unsigned char *p;