It turns out that OS X doesn't support long options for uname and it
doesn't support -o/--operating-system at all. Let's tweak uname's
options into something POSIX-compatible which still gives reasonable
results.
The new "uname -mrs" call results in the following:
OS uname -mrs
-----------------------------------------------
OS X Mavericks Darwin 15.2.0 x86_64
Ubuntu 14.04 Linux 3.13.0-32-generic x86_64
Without this, shell's printf is unreliable. For example, on OSX with
cs_CZ.UTF-8 locale it complained about number formatting:
tools/impact: line 51: printf: .0300: invalid number