Add a couple more changelog entries
fix compilation on Solaris 10 with GNU C 3.4.3

This patch fixes compilation on Solaris 10 platform which provides
GNU C 3.4.3 by default by removing unsupported -ftree-vectorize option.
This may penalize Solaris 11, where GNU C 4.6.2 is provided but current
cabal does not support OSes version detection and Solaris 10 is still
supported (by Oracle) and will be at least till 2021 so let's support it
too.
Bump version to 0.5.2.1