bad user experience if an array is provided to a File's path

I am trying to describe a tool that inputs many FASTQ files and outputs only one file. However, the cwltool fails when I define an array of File as input. I wrote a minimal example to reproduce this error using `cat` command.

`cat.cwl` file:

``` yml
cwlVersion: v1.0
class: CommandLineTool
baseCommand: [cat]
stdout: output.txt

inputs:
files:
type: File[]
inputBinding: {}

outputs:
output:
type: stdout
```

`cat-test.yml` file:

``` yml
files:
class: File
path: [file1.txt, file2.txt, file3.txt]
```

Command:

``` bash
cwl-runner cat.cwl cat-test.yml
```

Error:

```
/usr/local/bin/cwl-runner 1.0.20170413194156
Resolved 'cat.cwl' to '/home/welliton/cat.cwl'
Traceback (most recent call last):
File "/usr/local/bin/cwl-runner", line 9, in
load_entry_point('cwl-runner==1.0', 'console_scripts', 'cwl-runner')()
File "/usr/local/lib/python2.7/dist-packages/cwltool/main.py", line 753, in main
fetcher_constructor=fetcher_constructor)
File "/usr/local/lib/python2.7/dist-packages/cwltool/main.py", line 509, in load_job_order
normalizeFilesDirs(job_order_object)
File "/usr/local/lib/python2.7/dist-packages/cwltool/pathmapper.py", line 78, in normalizeFilesDirs
adjustFileObjs(job, addLocation)
File "/usr/local/lib/python2.7/dist-packages/cwltool/pathmapper.py", line 41, in adjustFileObjs
adjustFileObjs(rec[d], op)
File "/usr/local/lib/python2.7/dist-packages/cwltool/pathmapper.py", line 39, in adjustFileObjs
op(rec)
File "/usr/local/lib/python2.7/dist-packages/cwltool/pathmapper.py", line 75, in addLocation
parse = urllib.parse.urlparse(d["location"])
File "/usr/lib/python2.7/urlparse.py", line 143, in urlparse
tuple = urlsplit(url, scheme, allow_fragments)
File "/usr/lib/python2.7/urlparse.py", line 176, in urlsplit
cached = _parse_cache.get(key, None)
TypeError: unhashable type: 'CommentedSeq'
````

Is there any example of using an array of File as input? I followed the [user guide](http://www.commonwl.org/v1.0/UserGuide.html#Array_inputs).

Start with cwltool/pathmapper.py, especially normalizeFilesDirs, adjustFileObjs, and addLocation, then reproduce the failure with the shown cat.cwl, cat-test.yml, and cwl-runner command. Confirm that an array of File paths is accepted without the unhashable CommentedSeq error and that the cat example completes successfully.

Written by the indexing model from the issue text.