Fix file download error in cpac_install.sh

Possibly related to #388 

I attempted to use the automated install script and while it "worked" I ran into issues once trying to use C-PAC. It seems that it failed to download the cpac resources bundle, so none of those resources were available.

I traced it down to what I presume was a file rename.

Previously, script was attempting to download file named `cpac_image_resources.zip`, which no longer exists.

Instead, a similar file named `cpac_resources.tgz` now exists (and is referenced from [C-PAC Install Instructions](http://fcp-indi.github.io/docs/user/install.html#install-cpac-image-resources)). The directory contained within is still called cpac_image_resources, however, so subsequent `cd` commands are unaffected.

When unzipping the resources file on my system (Ubuntu 12.04) it throws a warning (`gzip: cpac_resources.tgz: decompression OK, trailing garbage ignored`) but still unzips successfully. If wrapped in a single tar command it throws additional output at the end that might seem more threatening to an end user 
```
tar: Child returned status 2
tar: Error is not recoverable: exiting now
```

I'm not sure if there's anything I can do via this pull request to address the quality of the .tgz file hosted at NITRC, though.


Because the .tgz file containing the patched download script is binary, I'm pasting the diff of the affected file below
(cpac_install.sh)
```
@@ -141,8 +141,8 @@
 #
 ##### Download and CPAC image resources #####
 echo '########## ACQUIRING CPAC IMAGE RESOURCES... ##########'
-wget http://fcon_1000.projects.nitrc.org/indi/cpac_image_resources.zip
-unzip cpac_image_resources.zip
+wget http://fcon_1000.projects.nitrc.org/indi/cpac_resources.tgz
+tar -xzvf cpac_resources.tgz
 cd cpac_image_resources
 cd ./symmetric
 # --- Move the templates to the FSL directory ---
```