Allow more controls in gmt clear

[PaulWessel]

This PR follows a suggestion in #7738 to allow the removal of just one data set, say earth_relief without deleting all the other Earth data. In addition I added option -N which simply lists (to stdout) which directories would have been deleted.

[Esteban82]

I got an error with -N

gmt clear data -N
ERROR: Caught signal number 11 (Segmentation fault) at
/lib/x86_64-linux-gnu/libc.so.6(+0xba2b7)[0x7f701b0ba2b7]
[0x0]
Stack backtrace:
/usr/local/lib/libgmt.so.6(gmt_sig_handler_unix+0xf1)[0x7f701b558b41]
/lib/x86_64-linux-gnu/libc.so.6(+0x42520)[0x7f701b042520]
/lib/x86_64-linux-gnu/libc.so.6(+0xba2b7)[0x7f701b0ba2b7]
/usr/local/lib/libgmt.so.6(+0x3f3e6)[0x7f701b43f3e6]
/usr/local/lib/libgmt.so.6(GMT_clear+0x1ce)[0x7f701b44031e]
/usr/local/lib/libgmt.so.6(GMT_Call_Module+0x4ff)[0x7f701b45e86f]
gmt(main+0x51b)[0x5583e8bcb8db]
/lib/x86_64-linux-gnu/libc.so.6(+0x29d90)[0x7f701b029d90]
/lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80)[0x7f701b029e40]
gmt(_start+0x25)[0x5583e8bcc7b5]

[PaulWessel]

Yikes. OK, that is fixed now but then there was another but so now my entire data dor os gone. Fixed that too but probably smart if you try this on a .server dir while renaming your original one .server_save and then just copy a few datasets to the temporary dir to see if it works. I am running gmt get data right now...

[Esteban82]

Now works. But I don't understand the error message (last one).

gmt clear data -N
clear [NOTICE]: Directories to be deleted if -N was not in effect:
/home/federico/.gmt/server/earth/earth_day
/home/federico/.gmt/server/earth/earth_relief/earth_relief_05m_p
/home/federico/.gmt/server/earth/earth_relief/earth_relief_01m_p
/home/federico/.gmt/server/earth/earth_relief
/home/federico/.gmt/server/earth
/home/federico/.gmt/server
clear [ERROR]: Unrecognized target - skipped

[PaulWessel]

I'll see if I can reproduce once gmt get stops...

[PaulWessel]

Strange since printing out the server directory is the last thing clear does so not sure what that means.

[PaulWessel]

OK, forgo to skip -N -V in the second loop (since I added a separate loop to detect -N).
Works for me now. See what you get.

[Esteban82]

Now it is fine.