CentOS build fixes for Upload Agent

* On systems where we do not build openssl from source (e.g. Ubuntu),
  curl should use plain --with-ssl instead of specifying the openssl lib
  dir
* Set OLD_KERNEL_SUPPORT for CentOS 5 builds (restoring LC_ALL hack
  dropped in 538233d)
* Do not build shared libraries for curl as the build is broken for them
  and we only use the static libraries anyway
* Makefile refactoring: extract variables CENTOS_MAJOR_VERSION and
  UBUNTU_VERSION
* Bump UA version to 1.4.8