cmTarget: Remove std::min and std::max MSVC6 compatibility code.

CMake is no longer required to build with MSVC6.
cmFindCommon: Remove MSVC6 workaround for nested struct private access.
cmStandardIncludes: Remove MSVC6 condition for cmArrayBegin macro.
cmSystemTools: Remove MSVC6 compatibility define.
VisualStudio: Remove MSVC6 compatibility macro.
cmGeneratorTarget: Remove MSVC7 workaround

Use partial specialization everywhere.
Help: Update developer manual with some C++ features now permitted.
cmTarget: Use clear and append on std::string.

To see if the dashboard now accepts it.
Merge topic 'remove-ancient-msvc-workarounds' into next

f39baea8 cmTarget: Use clear and append on std::string.
12cb0b86 Help: Update developer manual with some C++ features now permitted.
ba74465f cmGeneratorTarget: Remove MSVC7 workaround
41363c0c VisualStudio: Remove MSVC6 compatibility macro.
4efcfe52 cmSystemTools: Remove MSVC6 compatibility define.
5f4695cd cmStandardIncludes: Remove MSVC6 condition for cmArrayBegin macro.
7a064337 cmFindCommon: Remove MSVC6 workaround for nested struct private access.
fdb73547 cmTarget: Remove std::min and std::max MSVC6 compatibility code.