[showmount] implement long options

[eadler]

Summary

add long options support to showmount. Where mappings exist use the GNU
names for said options.

[kevans]

usr.bin/showmount/showmount.c

131 ↗

(On Diff #64846)

Generally when converting to long opts, we should use the '+' leading specifier to maintain preexisting behavior of getopt(3) of halting at the first non-option argument, unless it's really advantageous and we've documented the behavior change.

[eadler]

per @kevans

[eadler]

@kevans ping?

head/usr.bin/showmount/showmount.8

+======================================================================
+You installed Sverchok: the Blender add-on for architects and
+designers.
+
+You need to enable it in Blender: click on the "File" menu, then on
+the "User Preferences" sub-menu, click on "Add-ons", type in "sverchok"
+into the search box in the top-left corner, and check the "Sverchok"
+check-box to the right.
+
+Please consult the user's manual:
+http://nikitron.cc.ua/sverch/html/main.html
+======================================================================

head/usr.bin/showmount/showmount.c

+======================================================================
+You installed Sverchok: the Blender add-on for architects and
+designers.
+
+You need to enable it in Blender: click on the "File" menu, then on
+the "User Preferences" sub-menu, click on "Add-ons", type in "sverchok"
+into the search box in the top-left corner, and check the "Sverchok"
+check-box to the right.
+
+Please consult the user's manual:
+http://nikitron.cc.ua/sverch/html/main.html
+======================================================================