When a file is very large (more than 64KB of text), don't activate syntax highlighting by default. This should prevent us from wasting resources running pygmentize on enormous files.
Users who want the file highlighted can still select "Highlight As...".
The tricky part of this diff is separating the headers into "changeset" headers and "undershield" (rendering) headers. Specifically, a file might have these headers/shields:
- "This file is newly added."
- "This file is generated. Show Changes"
- "Highlighting is disabled for this large file."
In this case, I want the user to see "added" and "generated" when they load the page, and only see "highlighting disabled" after they click "Show Changes". So there are several categories:
- "Changeset" headers, which discuss the changeset as a whole (binary file, image file, moved, added, deleted, etc.)
- "Property" headers, which describe metadata changes (not relevant here).
- "Shields", which hide files from view by default.
- "Undershield" headers, which provide rendering information that is only relevant if there is no shield on the file.