Case insensitive sort function

Case insensitive sorting of a cell array of strings.

Matlab's SORT function returns first upper case contents and then lower case. SORTI will sort by alphabet without considering the case
For example
sort({'A' 'a' 'B' 'b'})
will return
{'A' 'B' 'a' 'b'}
while SORTI will return
{'A' 'a' 'B' 'b'}

25/3/2014 Update: Now also returns the index vector I as in the SORT function