versions: fix up error handling

Now we handle some things more explicitly and in the process get rid of
the blanket rescue on the mktemp block, which is something of an
antipattern.

By unloading the class *after* determining the version, we avoid the
case where the class had previously been unloaded but Formula.factory
failed, and trying to unload the nonexistent class results in a
NameError. Doing it this way, we avoid having to rescue NameError and
thereby avoid hiding other cases where it may occur.

We also rescue TypeError which gets us past a few more bad formula in
the history in some instances.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>

Library/Homebrew/cmd/versions.rb

@@ -63,21 +63,17 @@ class Formula
         path = Pathname.new(Pathname.pwd+"#{name}.rb")
         path.write text_from_sha(sha)
 
-        # Determine the version by loading the old class file.
-        # Note that this means that the command will error out after it
-        # encounters a formula that won't import. This doesn't matter
-        # for most formulae, but e.g. Bash at revision aae084c9db has a
-        # syntax error and so `versions` isn't able to walk very far back
-        # through the history.
-
-        # Unload the class so Formula#version returns the correct value.
+        # Unload the class so Formula#version returns the correct value
         # FIXME shouldn't have to do this?
-        Object.send(:remove_const, Formula.class_s(name))
         begin
-          nostdout { Formula.factory(path).version }
-        rescue SyntaxError
+          version = nostdout { Formula.factory(path).version }
+          Object.send(:remove_const, Formula.class_s(name))
+          version
+        rescue SyntaxError, TypeError
+          # We rescue these so that we can skip bad versions and
+          # continue walking the history
           nil
         end
-      end rescue nil
+      end
     end
 end