Cherry-pick "Merge branch 'PythonCxx17Fix-1.0-20190805' into '1.0'" into master

Python C++17 Fix, 1.0 branch (2019.08.05.)

See merge request !519 (merged)

(cherry picked from commit 2451e611)

• 4857bbb5 Removing the register keyword from the public Python headers.
• fea623ef Removed the patching of Python-2.7.15.
• 2dd375ba Re-organised the Boost build setup to use -Wno-register in C++17 mode.
• 2018aa7b Now explicitly setting the C++ standard for the HDF5 build.