Remove use of obsolete BOOST_EXPLICIT_TEMPLATE_TYPE{,_SPEC} macros.

[SVN r85894]
Remove use of obsolete BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE{,_SPEC} macro.

[SVN r85896]
Remove obsolete MSVC check from pragma guard

 git grep -h -B1 "^#\s*pragma once" | grep -v pragma | sort | uniq

is now clean.

[SVN r85952]