Allow passing multiple "includes"

[blimmer]

As implemented today, you can't pass multiple includes via a -i parameter. Each invocation of -i overwrites the last.

Here's the code that does that:

docker-protoc/all/entrypoint.sh

Lines 69 to 72 in 3a87206

	-i) shift
	EXTRA_INCLUDES="-I$1"
	shift
	;;

So, invocations like this don't work

docker run ... namely/protoc-all:1.11 -i protorepo -i something_else

It would be nice if each -i added onto the EXTRA_INCLUDES.

[blimmer]

I pushed this change to dockerhub if you'd like to test it out. the tag is:

blimmer/protoc-all:1.11-extra-includes