io.pipes: If dispose on in>> throws, then out>> leaks.
io.launcher: Fix two potential bugs.
1) If first (pipe) succeeds but second one fails, first pipe leaks.
2) out>> dispose fails, then in>> dispose is never called and leaks.
io.launcher: Fix bug -- if dispose fails, still call dispose on the other
resource.
sequences: change filter-as to allocate length of seq not exemplar.
destructors: more efficient dispose-each (not using make).
twitter: adding verify-credentials.
sequences.extras: change filter-index to use length of seq not exemplar.
sequences.extras: similarly improve map-filter and filter-map.
sequences.extras: adding index-selector.
units.imperial: adding more units.
units.imperial: fix minims.
spelling: fix splits and sorting of corrections, other cleanup.