Add length aware variant(s) of string hashing

- Being able to hash partial strings is needed for allowing string pool
  to operate on partial strings...

rpmio/rpmstrpool.c

@@ -61,6 +61,33 @@ static inline unsigned int rstrlenhash(const char * str, size_t * len)
     return hash;
 }
 
+static inline unsigned int rstrnlenhash(const char * str, size_t n, size_t * len)
+{
+    /* Jenkins One-at-a-time hash */
+    unsigned int hash = 0xe4721b68;
+    const char * s = str;
+
+    while (*s != '\0' && n-- > 0) {
+      hash += *s;
+      hash += (hash << 10);
+      hash ^= (hash >> 6);
+      s++;
+    }
+    hash += (hash << 3);
+    hash ^= (hash >> 11);
+    hash += (hash << 15);
+
+    if (len)
+	*len = (s - str);
+
+    return hash;
+}
+
+static inline unsigned int rstrnhash(const char * string, size_t n)
+{
+    return rstrnlenhash(string, n, NULL);
+}
+
 unsigned int rstrhash(const char * string)
 {
     return rstrlenhash(string, NULL);