ENT-12650 Use std::filesystem by default (#5)

To help move forward switch to using C++17 as target and use std
filesystem that comes with it. Add USE_BOOST_FILESYSTEM that will use
boost::filesystem (as previous) in case, but that defaults OFF. Note
change in API to pass paths by std::string so whichever filesystem is in
use does not bother the calling code.

ENT-12650 Missed another use of BOOST rather than Boost

ENT-12650 Remove conditional

This makes it more like old patch version

ENT-12650 Minor fixes to previous

EMT-12650 Further fixes

Particularly after trying USE_BOOST_FILESYSTEM=ON

ENT-3325 Further C++17 fixes (#4)

Remove uses of std::unary_function - this was deprecated at C++11
but has been formally removed at C++17. Seems the use was basically
redundant and can just be removed.

ENT-3325 Further C++17 fixes (#4)

Remove uses of std::unary_function - this was deprecated at C++11
but has been formally removed at C++17. Seems the use was basically
redundant and can just be removed.

ENT-3325 Further C++17 fixes

Remove uses of std::unary_function - this was deprecated at C++11
but has been formally removed at C++17. Seems the call was basically
redundant and can just be removed.

Ent 2470 update to be compliant with cpp17 (#3)

Replaced the use of auto_ptr to unique_ptr to be compliant with latest c++ standards.

ENT-2470: Changed auto_ptr to unique_ptr