Erroneous use of strip() can cause hasVoted to return False on issues that have been voted on

As the intent seems to be removing the .json ending from the issue ID, let's be strict about it and instead remove the last five chars if they are `.json`. Otherwise, issue IDs that do not conform to hexadecimals will have their j, s, o, and n bits cut out.
diff --git a/pysteve/lib/voter.py b/pysteve/lib/voter.py
index 43c1d70..dbc7242 100644
--- a/pysteve/lib/voter.py
+++ b/pysteve/lib/voter.py
@@ -48,7 +48,10 @@
     
 
 def hasVoted(election, issue, uid):
-    issue = issue.strip(".json")
+    # Cut away .json endings if found. This is seemingly only used with the file-based db backend.
+    # TODO: Test if this is still needed.
+    if issue.endswith(".json"):
+        issue = issue[:-5]
     return backend.voter_has_voted(election, issue, uid)
 
 def ballots():
@@ -101,4 +104,4 @@
        smtpObj.sendmail(sender, receivers, msg)         
     except SMTPException:
        raise Exception("Could not send email - SMTP server down?")
-       
\ No newline at end of file
+