Note bug janitors

One or more core developers spend one day per week mopping up accumulated mess in the bug tracking system. This includes:

• Initial triage: tagging, assigning, setting milestones, and eliminating incoming duplicates.
• Source alignment: making FIXMEs in code correspond to bug numbers and vice versa.
• Reproduction: checking locally to see if bugs are still valid.
• Followup: requesting clarification, testcases, etc. from reporters of unclear bugs.
• Actual fixing: if there's any time left, pick some work off that seems fixable in short order.

Janitors by day:

• Monday: @brson
• Tuesday:
• Wednesday: @graydon
• Thursday: @catamorphism (tjc on IRC)
• Friday: @pcwalton