proper context for resolve_tac, eresolve_tac, dresolve_tac, forward_tac etc.;
occasionally clarified use of context;

proper context for "net" tactics;
avoid implicit Tactic.build_net -- make its operational behavior explicit in application;

proper context for assume_tac (atac remains as fall-back without context);

avoid stepping outside of context -- plain zero_var_indexes should be sufficient;

renamed old-style Drule.standard to Drule.export_without_context, to emphasize that this is in no way a standard operation;

eliminated some old folds;

eliminated hard tabulators, guessing at each author's individual tab-width;
tuned headers;

explicitly qualify Drule.standard;

Merge.

use long names for old-style fold combinators;

Removed practically all references to Library.foldr.

Move towards standard functions.

Initial revision