Remove 'CYGWIN=check_case:strict', this does no longer work on

Cygwin 1.7.  Print warning if Automake version cannot handle
case insensitive filesystems.


git-svn-id: https://smartmontools.svn.sourceforge.net/svnroot/smartmontools/trunk@2808 4ea69e1a-61f1-4043-bf83-b5c94c648137