pyrap: Add HEAD repository
Make cmake build type more explicit

Explicitly set CMAKE_BUILD_TYPE in case we want to change it in
future, e.g. to add debug symbols. Bear in mind that the superenv
enforces a strict release build, so any other build needs the std env.
This is a straight refactor and should not change any installation.
meqtrees: Enable debug build

Since MeqTrees is still quite experimental it is useful to have debug
symbols included for tracing problems. The simplest way is to set the
cmake build type explicitly, replacing the default build type of None.
This also requires the std env as the superenv insists on stripping all
symbols. Use dsymutil to assemble symbol files for all libraries for
starters. This was inspired by mxcl/homebrew commit 00cf15ff23fd and
PR #12384.
meqtrees: Add debug symbols by default

Now also add debug symbols to optimised release build for easier
debugging via the cmake RelWithDebInfo build type. Bypass the use of
bootstrap_cmake script as it provides little extra functionality while
restricting the build type to Debug or Release only. Always follow
debug symlinks as they are the most complete set.