os_regex review

changes:
* replace octal values of charmaps with decimal ones (cause octal values greater than 127 causing conversion warnings)
* change string size variables to size_t
* rewrite OS_StrStartsWith() so that the length of the pattern  does not need to be computed
* enable unit test for regex extraction added by 79460acf9ae79dfd52de72c2599d6f0a3be81e83
* fix bunch of compiler warnings
* fix coverity warnings about uninitialized array (CID 28590)