SHA2 renamed to SHA256, SHA4 renamed to SHA512 and functions accordingly

The SHA4 name was not clear with regards to the new SHA-3 standard. So
SHA2 and SHA4 have been renamed to better represent what they are:
SHA256 and SHA512 modules.
diff --git a/programs/hash/sha2sum.c b/programs/hash/sha2sum.c
index 83124cf..81a8058 100644
--- a/programs/hash/sha2sum.c
+++ b/programs/hash/sha2sum.c
@@ -1,5 +1,5 @@
 /*
- *  sha2sum demonstration program
+ *  sha256sum demonstration program
  *
  *  Copyright (C) 2006-2011, Brainspark B.V.
  *
@@ -34,19 +34,19 @@
 
 #include "polarssl/sha2.h"
 
-#if !defined(POLARSSL_SHA2_C) || !defined(POLARSSL_FS_IO)
+#if !defined(POLARSSL_SHA256_C) || !defined(POLARSSL_FS_IO)
 int main( int argc, char *argv[] )
 {
     ((void) argc);
     ((void) argv);
 
-    printf("POLARSSL_SHA2_C and/or POLARSSL_FS_IO not defined.\n");
+    printf("POLARSSL_SHA256_C and/or POLARSSL_FS_IO not defined.\n");
     return( 0 );
 }
 #else
-static int sha2_wrapper( char *filename, unsigned char *sum )
+static int sha256_wrapper( char *filename, unsigned char *sum )
 {
-    int ret = sha2_file( filename, sum, 0 );
+    int ret = sha256_file( filename, sum, 0 );
 
     if( ret == 1 )
         fprintf( stderr, "failed to open: %s\n", filename );
@@ -57,12 +57,12 @@
     return( ret );
 }
 
-static int sha2_print( char *filename )
+static int sha256_print( char *filename )
 {
     int i;
     unsigned char sum[32];
 
-    if( sha2_wrapper( filename, sum ) != 0 )
+    if( sha256_wrapper( filename, sum ) != 0 )
         return( 1 );
 
     for( i = 0; i < 32; i++ )
@@ -72,7 +72,7 @@
     return( 0 );
 }
 
-static int sha2_check( char *filename )
+static int sha256_check( char *filename )
 {
     int i;
     size_t n;
@@ -110,7 +110,7 @@
 
         nb_tot1++;
 
-        if( sha2_wrapper( line + 66, sum ) != 0 )
+        if( sha256_wrapper( line + 66, sum ) != 0 )
         {
             nb_err1++;
             continue;
@@ -151,8 +151,8 @@
 
     if( argc == 1 )
     {
-        printf( "print mode:  sha2sum <file> <file> ...\n" );
-        printf( "check mode:  sha2sum -c <checksum file>\n" );
+        printf( "print mode:  sha256sum <file> <file> ...\n" );
+        printf( "check mode:  sha256sum -c <checksum file>\n" );
 
 #if defined(_WIN32)
         printf( "\n  Press Enter to exit this program.\n" );
@@ -163,12 +163,12 @@
     }
 
     if( argc == 3 && strcmp( "-c", argv[1] ) == 0 )
-        return( sha2_check( argv[2] ) );
+        return( sha256_check( argv[2] ) );
 
     ret = 0;
     for( i = 1; i < argc; i++ )
-        ret |= sha2_print( argv[i] );
+        ret |= sha256_print( argv[i] );
 
     return( ret );
 }
-#endif /* POLARSSL_SHA2_C && POLARSSL_FS_IO */
+#endif /* POLARSSL_SHA256_C && POLARSSL_FS_IO */