nox_main.cc: unused variable warning corrected.

Issue #15

Correcting compilation warning by wrapping reliable functionality under RELIABLE_ENABLED macro.

../../src/nox_main.cc: In function ‘int main(int, char**)’:
../../src/nox_main.cc:293:10: warning: variable ‘reliable’ set but not used [-Wunused-but-set-variable]
nox_main.cc: s/RELIABLE_ENABLED/UNRELIABLE_ENABLED/g

Issue #15

Correcting name of the macro according to review comments.
Merge pull request #16 from vitalivanov/issue-15

nox_main.cc: unused variable warning corrected.