textproc/hunspell: update to 1.6.0

• Restore DIST_SUBDIR from r305651
• Adjust license for "or later" clause
• Restore GPLv2+/LGPL21+ license files removed upstream as GPLv3+/LGPL3+ only affects Hunspell 2.0 (not currently built)
• Unbreak |make makepatch|

Changes: https://github.com/hunspell/hunspell/releases/tag/v1.6.0
PR: 215714
Submitted by: sunpoet (based on)
Exp-run by: antoine
MFH: 2017Q1
Differential Revision: https://reviews.freebsd.org/D8887