'calabash-ios console' command now tries find local .irbrc before falling back to the .irbrc in the scripts directory

i have many iOS projects using calabash.  in each one i use a custom '.irbrc' file - each project has a slightly different file. 

i really dislike having to type:  `CALABASH_IRBRC=.irbrc calabash-ios console`  when i want to drop into the irb.

the other option is to maintain a separate `irb.sh` for each project (which is my current solution), but that is just one more file to futz about with.

this is order in which the `IRBRC` is set:

1. `CALABASH_IRBRC` 
2. `./.irbrc` if it exists
3. the `.irbrc` file in the scripts directory