debian/lib/python/debian_linux/debian.py: Fix Version self-test failures

We didn't check for invalid characters in the upstream or revision
parts.  Tighten the regexps for those parts.

Also, failure to match the epoch or revision groups caused
those parts to be treated as part of the upstream version.
Split out the three parts and match them against separate
regexps.

debian/lib/python/debian_linux/debian.py

@@ -93,34 +93,30 @@ class Changelog(list):
                 top_match = bottom_match = None
 
 class Version(object):
-    _version_rules = r"""
-^
-(?:
-    (?P<epoch>
-        \d+
-    )
-    :
-)?
-(?P<upstream>
-    .+?
-)   
-(?:
-    -
-    (?P<revision>[^-]+)
-)?
-$
-"""
-    _version_re = re.compile(_version_rules, re.X)
+    _epoch_re = re.compile(r'\d+$')
+    _upstream_re = re.compile(r'[0-9][A-Za-z0-9.+\-:~]*$')
+    _revision_re = re.compile(r'[A-Za-z0-9+.~]+$')
 
     def __init__(self, version):
-        match = self._version_re.match(version)
-        if match is None:
+        try:
+            split = version.index(':')
+        except ValueError:
+            epoch, rest = None, version
+        else:
+            epoch, rest = version[0:split], version[split+1:]
+        try:
+            split = rest.rindex('-')
+        except ValueError:
+            upstream, revision = rest, None
+        else:
+            upstream, revision = rest[0:split], rest[split+1:]
+        if ((epoch is not None and not self._epoch_re.match(epoch)) or
+            not self._upstream_re.match(upstream) or
+            (revision is not None and not self._revision_re.match(revision))):
             raise RuntimeError(u"Invalid debian version")
-        self.epoch = None
-        if match.group("epoch") is not None:
-            self.epoch = int(match.group("epoch"))
-        self.upstream = match.group("upstream")
-        self.revision = match.group("revision")
+        self.epoch = epoch and int(epoch)
+        self.upstream = upstream
+        self.revision = revision
 
     def __str__(self):
         return self.complete