Treat declarations of pure virtual functions as definitions.
A pure virtual function won't (usually) have a definition.  Without one, we won't hyperlink
the name of the function where it is called.  As a workaround until we have better support
for (pure) virtual functions, we treat the declaration as a definition.
Merge branch 'testing' of https://github.com/mozilla/dxr into pure-virtual
Merge pull request #69 from abbeyj/pure-virtual

Treat declarations of pure virtual functions as definitions.