Add merge option for name conflict resolution
Make merging work correctly on Windows

xcopy expects full path and requires flag which disables overwrite
confirmation.
Remove useless check around replace_string()
Move prompt_what_to_do() in fileops.c

After its last invocation.

Additionally:
 * add a comment;
 * change * to [] in parameter list.
Propose merging only for two directories
Add copy with overwrite operation

Additionally add comments to functions and replace * with [] in argument
list.
Add move with overwrite operation

Additionally add comments and replace * with [] in parameter list.
Force destination file overwrite on dir merge
Document merge options for conflict resolution
Merge branch 'add-merge-option-for-conflict-resolution'

Add merge option for name conflict resolution.  It's displayed for
two directories only and allows for overwriting only files with matching
names instead of whole destination directory.