vector: fix transaction error msg

Import llvm tests for string.

test: remove redundant includes and fix comment

Imported from llvm-mirror/libcxx@88f5d7a38

Merge back changes from stable-1.5

Always initialize pmem::obj::array using double braces.

test: copy libcxx vector tests

test: rm unused file

vector: add comparison operators

Fix typo

Copy remaining libcxx vector tests.
Those test should be ported to test persistent vetctor.
Imported from llvm-mirror/libcxx@5ae92f0

transaction: add snapshot method

test/common/cont_test_common.hpp is as old file, we used to use
in tests for STL containers with persistent allocator

vector ctors

fix coverege travis output issue

travis output has 4MB limitation for an output and recently
it became a limitation for libpmemobj-cpp project

this patch removes llvm-cov output from travis log, but
coverage analysis are still being performed

Functions: begin(), end(), free_data(), size(), capacity()
are being used in ctors/dtor and tests.
This commit provides these functions as well.
Index access operators are added.

new method will allow user to manually snapshot memory range
within transaction

Using single braces initialization is allowed by the standard (C++11 §8.5.1/11),
however older versions of gcc (up-to 5.5.0) do not properly elide braces and
emit error in this case.

common: fix typo

cmake: replace unsupported boolean comparison

Imported from llvm-mirror/libcxx@5ae92f0

Modify pmem::obj::array tests

vector: fix _alloc() error handling

We need to cache pmemobj_tx_alloc return value and only after that
assign it to _data, because when pmemobj_tx_alloc fails, it aborts
transaction.

test: fix vector default ctor test

Even if we are removing created files in our test framework,
we should delete manually persistent pointers (for clarity sake).

it was not build previously