install-sh: avoid Tru64 sh `test' operator precedence issues. * lib/install-sh: Protect file names and directory components that consist of `=', `(', `)', or `!'. Move protection as early as possible, to avoid errors such as with Tru64 sh `test -z ='. * tests/instsh2.test: Extend test to cover more possibilities. Fixes 1.12 instspc-equal-install.test failure on Tru64/OSF 5.1. Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>