backport: Disable some libcxx tests for old g++ compilers.

They cannot be compiled due to lack of full C++11 support.

stable1.5: fix persistent ptr

This reverts commit 6bbb319e.

This reverts commit 0f0779d7.

Unlike buildds, there's no implied dependency on build-essential.
Can't use c++-compiler as gcc-snapshot provides it but doesn't ship an
alternative (#921877).

Decrease number of persistent_ptr dereferences by caching raw pointer.

Ref: #181

Fix argument parsing in examples/map_cli.

Fix range_snapshotting iterator when snapshot_size == 0

When snapshot_size == 0, no snapshotting should happen. This condition
must be explicitly checked inside range_snapshotting_iterator.

Parameters to iterator should specify range accessible by this
iterator. Before this patch those arguments described the whole
array instead of just the part from start to start + n.

argn was not incremented in case of get(). This resulted
in "invalid queue operation" message on every get.

Also fix "usage" for "insert" operation.

Ref: #186

Compile all of them, run&test scriptable ones.

map_cli fails but I strongly suspect a bug in the example code rather than
the actual library; reported upstream.

There's no binary library to link against.

Fix typo

common: fix typo

tests: change initialization of slice

gcc (7.3.0) gives array-subscript error when pointer to array is
decremented by 1.