spelling fixes

[ka7]

patch contains some spelling fixes ( just in comments ) as found by a bot ( http://www.misfix.org, https://github.com/ka7/misspell_fixer ). Any upcoming License changes (e.g. GPL2 to GPL3+) are hereby granted.

also seen lots of this

• protected final String getExtention(){
  vs.

• protected final String getExtension(){
  but don't want to refactor this.

[indication]

Thank you for checking spellings.
Your reviewed "getExtention" method would be fixed. ("getExtension" is the correct)