Various additions and fixes.

src/lib9/cistrstr.c

@@ -0,0 +1,23 @@
+#include <u.h>
+#include <libc.h>
+
+char*
+cistrstr(char *s, char *sub)
+{
+	int c, csub, n;
+
+	csub = *sub;
+	if(csub == '\0')
+		return s;
+	if(csub >= 'A' && csub <= 'Z')
+		csub -= 'A' - 'a';
+	sub++;
+	n = strlen(sub);
+	for(; c = *s; s++){
+		if(c >= 'A' && c <= 'Z')
+			c -= 'A' - 'a';
+		if(c == csub && cistrncmp(s+1, sub, n) == 0)
+			return s;
+	}
+	return nil;
+}