gcc 4 cleanups (mostly unsigned char* vs char*)

stralloc/stralloc_append.c

@@ -2,7 +2,7 @@
 
 /* stralloc_append adds one byte in[0] to the end of the string stored
  * in sa. It is the same as stralloc_catb(&sa,in,1). */
-int stralloc_append(stralloc *sa,const unsigned char *in) {
+int stralloc_append(stralloc *sa,const char *in) {
   if (stralloc_readyplus(sa,1)) {
     sa->s[sa->len]=*in;
     ++sa->len;