Merge back changes from stable-1.5

Change conversion operator from T() to T&() in v<>

persistent_ptr: add unsigned index operator 1.5

Ref: #103

Vector skeleton

Merge back changes from stable-1.5

Fix v swap, assignment operators and constructors.

Fix include in one more header

Fix headers inclusion for system headers 

Merge back changes from stable-1.5

Fix headers inclusion for system headers

Add info about pmemcheck annotations in readme

Fix ambiguous comments in make_persistent array

Changes are applied to files that were created after stable-1.5

Assignment operators didn't work correctly because operatorT()
was not really a const function and this_type (used in those functions)
was not decalared. This resulted in compile error while trying to
assign v<> of different types.

Additionally v<> constructor taking const T& as parameter is not
needed. Using it would mean assigning some value to underlaing val
in v<>, but first call to get() would run constructor (which would
potentially change the value).

Implement property that allows to subtract an iterator from another

Imported from llvm-mirror/libcxx@5ae92f0

Change breaking literals rule in clang.format

test: fix includes and flags

Add Valgrind annotation support

Add pmreorder support

and add test program to check if pmemobj supports COW for pool opening.
COW for reorder tests is needed because if checker program does any recovery
(for example in pool::open) this is not logged and will not be reverted by
pmreorder. This results in unexpected state in proceding pmreorder steps
(expected state is initial pool, modified only by pmreorder)