update version number to 2.6.0-pre
Change output formats from octal to hexadecimal
Removed deprecated 'register' storage class specifier.
clang-3.5.0 now complains about them: warning: 'register' storage class specifier is deprecated [-Wdeprecated-register]
Add disambiguation braces in main.c
Fix warning on assigning from `const char*` to `char*`
Allow error reporting routines to accept varying number of arguments in modern style