Revert "allow uppercase letters in jar names"

This reverts commit 2d530aa.

See
https://maven.apache.org/guides/mini/guide-naming-conventions.html
and #50

src/clojars/db.clj

@@ -208,8 +208,8 @@
                   :version    version})))
 
 (defn add-jar [account jarmap & [check-only]]
-  (when-not (re-matches #"^[a-zA-Z0-9-_.]+$" (:name jarmap))
-    (throw (Exception. (str "Jar names must consist solely of "
+  (when-not (re-matches #"^[a-z0-9-_.]+$" (:name jarmap))
+    (throw (Exception. (str "Jar names must consist solely of lowercase "
                             "letters, numbers, hyphens and underscores."))))
   (transaction
    (if check-only
@@ -234,4 +234,4 @@
                       (or offset 0)]]
                     :results)]
     ;; TODO: do something less stupidly slow
-    (vec (map #(find-jar (:group_name %) (:jar_name %)) r))))
+    (vec (map #(find-jar (:group_name %) (:jar_name %)) r))))