user hooks WIP
add Registry.cursor_db class type and corresponding implementation in store
added some TODOs to registry.ml
clean up registry store interface. change Simple_store.delete semantics to no longer throw Not_found.
supply current Interval.t to user functions/hooks
add consistency to user_hook call
nodes shouldn't die when they can't find a user function
fix test_user_function
test user_hook
allow continuing with any client change from user-hook
more powerful user hooks
add fold_(rev_)range helpers for user hooks + feedback from PR
add test for Registry.Cursor_store helper
Merge pull request #379 from Incubaid/user-hooks2

User hooks2
Merge pull request #391 from Incubaid/1.7

1.7 for 1.8
Merge branch '1.7' into 1.7-for-1.8

* 1.7:
  Check for ENOSPC conditions at startup
  fix typo
  logging for 'close'
  turn 2 bools into 1
  make sure we get the 0xfe
Merge pull request #396 from Incubaid/1.7-for-1.8

1.7 for 1.8
Remove some old files & scripts
Merge pull request #405 from Incubaid/clean_tree

Remove some old files & scripts
Merge branch '1.7' into 1.7-for-1.8

* 1.7:
  Remove unused `Catchup.store_tlc_cmp` type
  Re-instate 'bisect' builds
  Enable all warnings, most as errors, and fix errors
  Enable warning 32 "Unused value declaration"
  Enable compiler warnings
  Remove dead code
  jenkins twiddling
  added ad hoc test for client_lib
  added missing dependencies (no, I'm not happy with these dependencies)
  more logging in validate_dir + make fsync of touched file depend on _fsync_tlog_dir
  fixed typo in cmdline output of --run-system-tests
  fix test_copy_db_to_head
  prevent drop master test from failing with NoMaster because in the beginning the active master was stopped
Fix build

Extra warnings enabled through d4a8da5aaa686dfb96d05dc394282188b13d6218 trigger
build errors. This commit fixes these.