The folder is located just in the base dir of your SDcard:
Since Textsecure is now called Signal, there is no extra folder. It is located directly in your SDcard home folder:
Note: sometimes the phone doesen't show the folder on your computer, then you could use a filemanager on your phone (like ...
Install the Google package for your custom ROM. For instance cyanogenmod you flash the ROM then the Google package, ask whoever made the ROM for the correct version you need, most developers would put instructons in the first topic in their thread.
I can't explain what 'srv_listen' really does but to find more info you can use the infobutton in Xprivacy next to the permission name.
There you will find that the actual permission is called ACCESS_COARSE_LOCATION and you'll find a link to the Google documentation.
I'm sorry that I can't help more.
If you go through your apps list you can see all the apps that have permission to send texts (or you could use appops to save having to click on every app), you can then narrow it down based on how reputable the app is, and/or doing web searches, once you thing you have narrowed down the app you can either, uninstall the app or block the permission using app ...
Like Chahk said, the folder is /sdcard/TextSecureExport. I've had trouble accessing it (even after moving it) over the camera-centric USB interfaces.
I ended up compressing the file to a Zip archive using ES File Explorer and then using Google Drive to browse and upload the file. This also makes it easy to pull back down to a different device or after ...