RHEL5 support

Hi,

Following on from #10, I've attempted to add support for building and using clj-v8 with RHEL5 distros. This is an older but still stable and widely-used platform, and it required a number of changes:

* Build shell scripts using sed more portably (no -E flag available).
* A new "linux-rhel5" build target that's similar to distinct from "linux", and for x86_64 only.
* RHEL5 detection using `lsb_release` where available, including CentOS.
* JNA dependency bumped to 3.5.2, which relaxes its glibc dependency version (accepts pre-2.11).
* Additional binary builds of v8 with these changes (using CentOS 5.10).

Thoughts?