ncurses: Add libcurses symlink to libncurses

Some packages use -lcurses when they are linking, so they try to link to
a library called libcurses. The library provided by our ncurses package
is called libncurses, so those packages fail to link with a message like
this one:

/bin/ld: cannot find -lcurses

Installing a libcurses symlink to libncurses fixes the problem.

Fixes:
  http://autobuild.buildroot.net/results/466/466995f9534447a4f54327a14c44ef9e16dd1123/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: Markos Chandras <Markos.Chandras@imgtec.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>