Database: custom parser cache

[lahwaacz]

• recomputable tables from MediaWiki (info only for the latest revisions)
• implement a function to recursively expand templates transcluded on a page
• parse latest revisions and cache data in these tables:
  • pagelinks
  • templatelinks
  • imagelinks
  • categorylinks
  • langlinks
  • iwlinks
  • externallinks
  • category (discarded - tracks only the number of category members, which can be found online from joins)
  • redirect
• recursive per-page invalidation
• implement select queries for these tables
  • pagelinks (prop=links, prop=linkshere)
  • templatelinks (prop=templates, prop=transcludedin)
  • imagelinks (prop=images)
  • categorylinks (prop=categories)
  • langlinks (prop=langlinks)
  • iwlinks (prop=iwlinks)
  • externallinks (prop=extlinks)
  • redirect (prop=redirects)
• cache custom info specific to wiki-scripts:
  • section headings (useful for e.g. link-checker.py)
  • follow-up in Tracking renamed sections #36