don't modify missing header arguments during merge

* lisp/ob-core.el (org-babel-merge-params): More careful to check that
  the colname- and rowname-names header arguments exist during merge.
check html-link-home exists before triming

  Ensure that the :html-link-home property exists before passing it to
  `org-trim' which assumes it's argument is a string.
ob-core remove-if -> org-remove-if

* lisp/ob-core.el (org-babel-merge-params): Replace remove-if with
  org-remove-if.
o org-clock.el (org-clock-notify-once-if-expired): Honor `org-clock-sound'

* org-clock.el (org-clock-notify-once-if-expired): Honor
`org-clock-sound'.

TINYCHANGE
Merge branch 'maint'
ox: Preserve coding system when writing output to a file

* lisp/ox.el (org-export-to-file): Preserve coding system when writing
  output.
Merge branch 'maint'