Clean up string handling.

Clean up string handling.

* lisp/org-compat.el (string-prefix-p, string-suffix-p):
Add compatibility definitions for 24.3.

* lisp/ob-R.el (org-babel-edit-prep:R):
* lisp/ob-core.el (org-babel-demarcate-block):
* lisp/ob-js.el (org-babel-js-read):
* lisp/ob-latex.el (org-babel-execute:latex):
* lisp/ob-ref.el (org-babel-ref-parse):
* lisp/ob-shell.el (org-babel-variable-assignments:shell):
* lisp/org-protocol.el (org-protocol-create):
* lisp/org-table.el (org-table-field-info):
* lisp/org.el (org-get-buffer-for-internal-link):
* lisp/ox-publish.el (org-publish-compare-directory-files):
* lisp/ox-texinfo.el (org-texinfo-template):
Use `string-{suffix,prefix}-p' instead of `string-match(-p)'.

* lisp/ob-python.el (org-babel-python-read-string):
Ditto, also use `substring' rather than `match-string'.

* lisp/org-table.el (org-table-copy-down):
(org-table-insert-hline, org-table-current-field-formula):
(org-table-get-formula): Use `string-match-p' instead of
`string-match'.