One should not change the program arguments!
This change also reduces warnings from the icc compiler.

Almost all changes are just syntax changes (adding const to
'get_one_option function' declarations).

Other changes:
- Added a few cast of 'argument' from 'const char*' to 'char *'. This
  was mainly in calls to 'external' functions we don't have control of.
- Ensure that all reset of 'password command line argument' are similar.
  (In almost all cases it was just adding a comment and a cast)
- In mysqlbinlog.cc and mysqld.cc there was a few cases that changed
  the command line argument. These places where changed to instead allocate
  the option in a MEM_ROOT to avoid changing the argument. Some of this
  code was changed to ensure that different programs did parsing the
  same way. Added a test case for the changes in mysqlbinlog.cc
- Changed a few variables that took their value from command line options
  from 'char *' to 'const char *'.