Fixed a build bug that would trigger pulling of 3rdparty code every time

Even if the code shouldn't be rebuilt (i.e. when the `built_flat' file is present), the repository for 3rdparty/json-c code would still be updated. This isn't happening anymore now.
Added support for optional floating point precision into time string generation
Removed debug output
Added config option to the `symboliclog' plugin for floating point timepoints

The `symboliclog' plugin now features an individual configuration option `time-precision' that controls with which floating point precision time strings are generated. If the value is left out or set to zero, no floating point precision is generated (i.e. timepoints are integers). If a number is given, that many decimals are used for precision.
Changed the default list of plugins to load and added symobliclog time precision
Added gmon.out to .gitignore