Fixed compiler warnings found by buildbot

Makefile.am:
  Removed extra empty line
cmd-line-utils/libedit/sys.h:
  Fixed that strndup() doesn't give compiler warnings
mysql-test/Makefile.am:
  Fixes for 'make distcheck'
plugin/auth_pam/auth_pam.c:
  Ensure that prototype for strndup() is included on linux
sql/share/Makefile.am:
  Fixes for 'make distcheck'
storage/innodb_plugin/btr/btr0sea.c:
  Fixed compiler warning
support-files/Makefile.am:
  Fixes for 'make distcheck'