Fix some 'test' failures when running 'make install'. When shell variables are unexpectedly empty, 'test' gets the wrong number of arguments and becomes unhappy. Logical AND should not be done with 'test EXPR1 -a EXPR2' in such cases, because 'test' logic does not short-circuit. Replace with 'test EXPR1 && test EXPR2'. Shell logic does short-circuit, and if the first test invocation fails, the second will never occur, and will never encounter missing arguments.