Move trash file existence check to trash.c
Prettify declarations in the trash unit

* Add empty lines.
* Use [] instead of * for arrays.
Introduce exists_in_trash() function

Checks whether file with given name exists in the trash directory.
Move gen_trash_name() to trash.c

Generates unique name for a file in a trash directory.
Move trash related logic to trash.c
Improve get_real_name_from_trash_name() function
Fix possible rm -rf at dst on manual restoring

Was unlikely, but possible situation, only with files that were put
there manually.
Store absolute paths of trashed files in vifminfo
Path original directory name to gen_trash_name
Extract trash creation into a function

To separate actual creation from interaction with a user.
Add get_mount_point() function

Fills given buffer with path to mount point of the path.
Prefer to use trash in mount root
Better code for commands.c:restore_cmd()
Make 'trashdir' option to be list of strings

Was a string.
Use until_first() in get_attrs()
Use skip_char() in info.c:get_sort_info()
Add 'trashdir' values extraction and validation

By the way moved some of trash related functions from cfg/config to
trash.c and updated places where they are used.

Extracted values are stored in static variables of trash module.
Use set_trash_dir() to ensure trash dirs exist
Hide create_trash_dir() function

Not used outside trash module anymore.
Rename trash_dir_is_ok() to validate_trash_dir()

Change is caused by the fact that the function might create a
directory.