Corrected path of popup window in Select Location.

Issue : Adding/Updating lat-long custom field manually using 'select' button of tkgmap plugin we see a pop-up window opens without the map with following error message :
"Not Found The requested URL /tkgmap/window was not found on this server."

Cause : Popup window shows incorrect path in address-bar localhost/tkgmap/window
Fix : Popup window should show correct path in address-bar : localhost/redmine/tkgmap/window

Details : Note: See #3 for detailed explanation.
Bug is caused due to a location/configuration bug by the plugin author.
Normally redmine shows up on the URL like so : http://test-site.com/redmine/issue/16
But redmine can be configured to hide the 'redmine' part of URL like so : http://test-site.com/issue/16

See : How to change default URL for Bitnami Redmine : http://wiki.bitnami.com/Applications/BitNami_Redmine#How_to_change_the_default_URL_to_the_root.3f

The plugin author @shota-kobayashi seems to have developed on such a configured machine.
Installing on a plain-vanilla machine the routing using URL was failing due to incorrect path.
Adding back the 'redmine' fixed the issue in the code. 

Note : On windows /redmine/ is aliased to apache accessible folder "htdocs/public" in "redmine\conf\httpd-prefix.conf". So /redmine/tkgmap/window maps out to fully expanded path properly.
```
Alias /redmine/ "C:\BitNami\redmine-2.4.1-1/apps/redmine/htdocs/public/"
Alias /redmine "C:\BitNami\redmine-2.4.1-1/apps/redmine/htdocs/public"
```

Now it's possible to select/update the location for a given issue in Redmine.