Update Makefile

1. Preserve the timestamp by replacing cp with install -p
2. Restrict file permissions by install -m
mkdir -p $(DESTDIR)$(SYSCONFDIR)

mkdir -p $(DESTDIR)$(SYSCONFDIR)
Update $(DESTDIR)$(PREFIX) in comments

--- we always install to PREFIX/etc.
+++ we always install to $(DESTDIR)$(PREFIX)/etc.
Merge branch 'patch-1' of github.com:cicku/julia into cicku-patch-1

Conflicts:
	Makefile
INSTALL_B does not exist. Use INSTALL_M instead.