The rationale for these new behaviors is as follows:

We now allow existentials to be unpacked in local (but not top-level!)
ValBinds, so some pattern signatures that used to fail in the renamer
now fail in the type checker (if the type of the body mentions the
unpacked type var):
   tc141(normal)

We don't always print HsWrappers in debug mode:
   TH_exn1(normal)
   TH_exn2(normal)

Sections are parsed (and therefore printed) differently:
   rnfail019(normal)
   read023(normal)

Character numbers in pattern printing are more precise:
   tcfail067(normal)
   tcfail124(normal)
   tcfail125(normal)