hex_dump_string function for debug output

will be used to dump UTF-8 and binary strings, showing non-ascii and control characters. UTF-8 represented as binary string (with special UTF-8 indicator appended to string). should also work with broken UTF-8
improve hex_dump_string

escape some control characters as perl escapes (tab, cr, lf) + quote entrie string + escape quotes and backslash
hex_dump_string - bug in test fixed
Begin of Warnings/Errors/Fatals rework

1) 'confess' now produces "UNEXPECTED ERROR" with a stacktrace and return code 1
2) 'die(exception(message))' now produces 'Fatal error' message and return code 1
3) "FATAL ERROR" has a suffix: empty string, parent (i.e. after fork()) and 'child'
4) Errors will now terminate children with SIGUSR2
5) Some code added to Utils to process errors and messgaes
6) SIG{DIE} removed, errors catch done now using eval{}
7) there are several error catch blocks - default, after fork and in children
8) one typo fixed in variable name
9) 'OK DONE' now always (i.e. for all commands) printed in case of success
rework and unit test for invalid characters in filename exception