parsedate: abort on negative dates (issue2513)

catches "hg commit -d '-7654321 3600'" (example)

mercurial/util.py

@@ -1116,6 +1116,8 b' def parsedate(date, formats=None, defaul'
     # to UTC+14
     if abs(when) > 0x7fffffff:
         raise Abort(_('date exceeds 32 bits: %d') % when)
+    if when < 0:
+        raise Abort(_('negative date value: %d') % when)
     if offset < -50400 or offset > 43200:
         raise Abort(_('impossible time zone offset: %d') % offset)
     return when, offset

tests/test-commit.t

@@ -22,6 +22,9 b' commit date test'
   $ hg commit -d '111111111111 0' -m commit-7
   abort: date exceeds 32 bits: 111111111111
   [255]
+  $ hg commit -d '-7654321 3600' -m commit-7
+  abort: negative date value: -7654321
+  [255]
 
 commit added file that has been deleted