This reverts commit 6047e3ce.

This reverts commit bcd87965.

See https://github.com/miloyip/rapidjson/commit/a2a0d161#commitcomment-9838110

Some compilers warn about the missing initialisation of the std::exception
base class of the AssertException helper.  The simplest solution is to
inherit from std::logic_error instead, which provides all of the required
functionality already.

Note it redefines RAPIDJSON_ASSERT() to throw exception in unittest and
check for assertion with gtest.

There are two copies of `StrLen` in the RapidJSON code base
 * strfunc.h: rapidjson::internal::StrLen<Ch>
 * unittest.h: Strlen<Ch>

To hide a warning on MSVC, align both implementations to use
'unsigned/SizeType' as return type and add an explicit cast.

Warning push/pop support has been added to GCC in version 4.6.0,
and pragmas to ignore certain warnings are present since 4.2.0.
This patch hides the compiler-specific warning push/pop/disable
pragmas behind a macro-based implementation (currently for MSVC and
clang /GCC.

This avoids warnings, as seen e.g. on GCC 4.4:
  ../../include/rapidjson/document.h:14: error: expected [error|warning|ignored] after ‘#pragma GCC diagnostic’
and earlier versions complaining about unknown pragmas being ignored.

Note: unittest.h and perftest.h need to check for compilers
explicitly, as rapidjson.h is not included there.

tmpnam() in VS prepends backslash in the path.

git-svn-id: https://rapidjson.googlecode.com/svn/trunk@2 c5894555-1306-4e8d-425f-1f6f381ee07c