Implement in-place inject-as-head

Conflicts:
	extension/server/ArakoonManagement.py
	extension/test/server/shaky/test_inject_as_head.py
	src/main/main.ml
	src/node/dump_store.ml
Add some labels to bool arguments

As requested during review of Incubaid/arakoon#313.

See: https://github.com/Incubaid/arakoon/pull/313

Conflicts:
	src/main/main.ml
	src/node/dump_store.ml
Merge pull request #315 from Incubaid/inplace-iah-1.6

Implement in-place inject-as-head