Don't detect indentation when in Makefile2/Automake syntax

Same as the default Make syntax shipped with sublime does. Otherwise
you can get in a weird state where you have some spaces in a Makefile,
so sublime detects you want spaces instead of tabs, and suddenly its
impossible to type a proper tab into you makefile

You never want to translate tabs to spaces in make, so we shouldn't
try to detect spacing
Merge pull request #2 from mattdangerw/dont-detect

Don't detect indentation when in Makefile2/Automake syntax