when exporting curve coordinates to X9.63 format, perform additional sanity checks on input

Reported by Sean Burford.
doc update
bumped version
testcompat: updated
treat GNUTLS_E_GOT_APPLICATION_DATA as non-fatal if initial negotiation is complete

This corrects a regression introduced in b5a0de2e6da98866cafb770c3141b7353d030ab2
Reported by Dan Winship. https://savannah.gnu.org/support/?108690
tests: added test for GNUTLS_E_GOT_APPLICATION_DATA on rehandshake

Conflicts:
	tests/Makefile.am
doc update
restore only the documented behavior
corrected memleak in read_key_mem()

Patch by Georg Richter.