init.sh: accommodate even those who specify bogus srcdir manually * tests/init.sh: Normally, srcdir is guaranteed by automake and configure-time tests to be sanitized, so that there is no need to use "$srcdir" in Makefile rules and shell scripts. Using $srcdir (with no double quotes) suffices. However, since tests may be invoked manually, and since you may explicitly set srcdir to the name of a directory containing spaces, do quote its uses here. * tests/test-pread.sh: Likewise. Suggested by Bruno Haible.