add result-file-exists check

test succeeds when result-file does not exist before.
sort out ignore patterns
add result-file-exists check(fix #4)

test succeeds when result-file does not exist before.
Merge commit '3d99a243427a75ff9444eded1950c71e2f91adcb'
add CONTRIBUTORS
dtl-1.16 released
fix typo
modified Copyright
fixed typo
fix problem(get_current_dir_name is not in Mountain Lion)
remove version number  in head comments
add version string to variables.hpp
dtl-1.17 released
remove files related mercurial
remove warning related constructor-initializer's order
fix typo
add printSES function for custom Printer

Patched by Hu Shubin
add strdiff_cp
update COPYRIGHT
dtl-1.18 released