Pre-parse output attribute declarations

[jzavala-gonzalez]

When declaring new output attributes using the 'output-attribute' keyword, XULE needs to incorporate these new keywords into its grammar before it can parse the remaining file. Otherwise, it crashes when seeing a "new" keyword. This is particularly necessary when using XINCE because all the attributes it needs declared. Also, I copied over these edits directly from my site-packages installation so I might miss something just let me know.