Flexible kern names

[tristangdwl]

Some friends recently requested that we add support for redundant kernel names e.g. 'cp' and 'cprime' to the .kern files, unifying the notation with the kernel constructors.

At the same time, I added 'all', 'trans_rep', 'trans_rep_prime', 'c2trans' to kernel constructors for helm2d, helmd2dquas, 'helm2diff'.

Added alternate names

• 'all', 'trans_sys', 'tsys'
• 'trans_rep', 'trep'
• 'trans_rep_p', 'trep_p'
• 'c2trans', 'c2t', 'c2tr' <- Should we add support for s2trans and d2trans at the same time?
• 'stau', 'st'
• 'cgrad', 'cg' (and same for s and d)

Also added a test that helm2d.kern etc.. interleave correctly, i.e. that 'all' is really [D,S; C', S']

[askhamwhat]

All looks good.