NumberParser::parseUnsigned should not parse negative numbers

The function should abort if a negative number (e.g. "-123") is passed as input
Merge pull request #433 from siemens/numparser

NumberParser::parseUnsigned should not parse negative numbers
fixed GH #410: Bug in JSON::Object.stringify() in 1.5.2
make trySleep test a bit more stable
cmake: added missing sources to CMakeLists.txt - fixes missing symbol errors
Merge remote-tracking branch 'upstream/develop' into develop
Merge pull request #434 from guruofquality/cmake_source_list_fixes

cmake: added missing sources to CMakeLists.txt
- fixed GH #362: Defect in Var::parseString when there is no space between value and newline
- fixed GH #314: JSON parsing bug
- added GH #313: MetaColumn additions for Data::ODBC and Data::SQLite
GH #416: PDF::Page::createTextAnnotation bad comparison
GH #379: Remove unnecessary null pointer checks
GH #346: Make Poco::Data::Date and Poco::Data::Time compare functions const.
GH #341: Compiling poco-1.5.2 for Cygwin
GH #305: There are bugs in Buffer.h
GH #321: trivial build fixes (BB QNX build)
Merge remote-tracking branch 'upstream/develop' into develop