Remove some dead code from codegen as found by pyflakes.
Remove unused references to jsids in the generated code for dictionaries.
auto merge of #2156 : Ms2ger/servo/codegen-deadcode, r=jdm
Support running make check-wpt with the objdir in less common places.
Use 'exceptionCode' when converting to DOMString.

This change allows us to use the code even in cases where we return a
Result type rather than a JSBool. Interface, primitive and union types
already get this right.
Merge the 'new' and 'Init' functions for dictionaries.

This moves the code in callers more in line with conversions for other types
and ensures the default values given to the dictionary fields (as defined by
the defaultValue function in CGDictionary.impl) do not escape the 'new'
method. The new code is also more in line with the code used by the
FromJSValConvertible trait.

This is the first step of my planned rewrite of the dictionary initialization
that will remove the default values entirely and reduce the code
duplication in the 'Init' (now 'new') function.
auto merge of #2162 : Ms2ger/servo/wpt-objdir, r=jdm
Put _virtualenv in the build dir, not the objdir
auto merge of #2163 : Manishearth/servo/wptfix, r=Ms2ger

#2162 was a tad off, it moves the virtualenv to the object directory (x86_64-unknown-linux-gnu, etc) instead of the build directory (build/, or whatever you're using). This moves it back. (Otherwise the `clean-wpt` target won't work)
auto merge of #2164 : Ms2ger/servo/dictionary-init, r=jdm