v2016.04.07, rebackgui, warnings found by clang

v2016.04.07, rebackgui, warnings found by clang

rebackgui:
* test of symbolic link before test of directory
* allows being root by setuid()
* translation improvements
* documentation in rebackgui.html
lib:
* file copy under linux:
** copying symbolic links
** setting owner and group
* linux: using QT setpermissions() instead of chmod()
* new: modifyToNonExisting()
* ReLogger(): correction of logging file "ring" (incrementing numbers,
  limited count of files)
* ReProcess::executeAndRead(): timeout
* added: I18N::b2s()
* more tests
* uint64_t changed to quint64
* ReGuiApplication(): default base dir is now <home>/.reappl