config: abort on indented non-continuation lines (issue1829)

Previously, as soon as a continuation would be met, "cont" would stay
forever set to True, but "item" was set back to "None".
This caused the continuation code bits to run every time, until the next
"self.get(section, item) + '\n'" which would crash.

mercurial/config.py

@@ -93,6 +93,7 b' class config(object):'
                     self.set(section, item, v, "%s:%d" % (src, line))
                     continue
                 item = None
+                cont = False
             m = includere.match(l)
             if m:
                 inc = m.group(1)