cleanups in stralloc and buffer:

int -> long for sizes
    char -> unsigned char for strings

stralloc/stralloc_diff.3

@@ -9,5 +9,7 @@ int \fBstralloc_diff\fP(const stralloc* \fIa\fR,const stralloc* \fIb\fR);
 stralloc_diff returns negative, 0, or positive, depending on whether
 \fIa\fR is lexicographically smaller than, equal to, or greater than the
 string \fIb\fR.
+.SH "RETURN VALUE"
+<0 if a<b, 0 if a==b, >0 if a>b.
 .SH "SEE ALSO"
 stralloc_diffs(3), stralloc_starts(3)