Implement iop_rmfile()
Use unlink() in ior_rm for non-directories

For safety reasons.
Add io/ior.c:XXX to consider in future
Fix wrong indentation in src/utils/fs.c
Rename fileops:{ entry_is_dir => is_dir_entry }()
Make utils/fs.c:entry_is_dir() public

Uses dentry or full path to check file type.  Symbolic links are
_not_ dereferenced.
Implement iop_cp() with basic unit-tests
Finish writing unit-tests for iop_cp()
Use common setup/teardown in ior unit-tests
Remove iop_mv()

ior_mv() covers all possible cases, no need for iop_mv(), which would
depend on ior_cp() for cross mount points file moving.
Initial implementation of copy on system calls
Add CRS to implement directory merging on ior_cp()

CRS -- Conflict Resolution Strategy
Add utils/fs:is_in_subtree()

Checks that entity pointed to by the path is located under the root
directory.
Forbid copying dir inside itself
Extract some common functions of ior/ tests
Implement ior_mv()
Enable use of ior_mv() and ior_cp() in Vifm
Fix iop_mkdir() and absolute path
Extend split_and_get() to help with `mkdir -p`
Use split_and_get() in iop_mkdir()