Take raiseHttpErrors into account on submit

If an HTTPError is raised on `browser.submit`, it should only be
reraised to the user if `browser.raiseHttpErrors=True`.

This behavior already applies to `browser.open`, thus it is expected to
apply to `browser.submit` as well.

src/zope/testbrowser/browser.py

@@ -797,6 +797,10 @@ def submit(self, label=None, name=None, index=None, coord=(1,1)):
                 try:
                     try:
                         self.browser.mech_browser.open(request)
+                    except mechanize.HTTPError, e:
+                        if self.browser.raiseHttpErrors:
+                            fix_exception_name(e)
+                            raise
                     except Exception, e:
                         fix_exception_name(e)
                         raise