mpkg: do_install: prompt to flag already installed package.
mpkg: do_install: prompt to flag already installed package.

If a package is already installed to satisfy dependencies of an other package,
ask user to flag it as user-installed.

Signed-off-by: Gaël PORTAY <1666f60cfa201a60b0ea694168a0b6932673170a@gmail.com>

gazoo74/mpkg,gazoo74/mpkg