Add m_ prefix for the string API

tests/fail-no-oplist.c

@@ -80,7 +80,7 @@ ILIST_DEF(tmpstr, tmp_str_t, DEFAULT_OPLIST)
 #include "m-string.h"
 void f(void)
 {
-  M_LET(x, M_STRING_OPLIST) {
+  M_LET(x, M_M_STRING_OPLIST) {
   }
 }
 

tests/test-mstring.c

@@ -611,7 +611,7 @@ static void test0(void)
   string_set_str (s1, "");
   assert (string_capacity(s1) > 0);
   string_reserve (s1, 0);
-  assert (string_capacity(s1) == sizeof (string_heap_ct) - 1);
+  assert (string_capacity(s1) == sizeof (m_string_heap_ct) - 1);
   
   string_set_str(s1, "HELLO XXX!");
   string_replace_at(s1, 6, 3, "World");