Adaption for Fedora packaging.

1. Preserve the timestamp.(Will help people to see the real time of files were generated)

2. Correct the permissions for standard. As far as I can tell you, 755 is the standard for binaries and 644 is the standard for non-executable files.

3. Add DESTDIR support as RPM needs to install files to a pseudo folder first which doesn't need to be granted any root access like /usr, and when we build RPMs we never use root to build.

PS: I'm packaging pgpdump for Fedora.
Merge pull request #4 from cicku/patch-1

Adaption for Fedora packaging.