org-element: Fix $...$ fragments followed by an apostrophe

* lisp/org-element.el (org-element-latex-fragment-parser):
* lisp/org.el (org-latex-regexps): Allow an apostrophe right after
  a fragment.

* testing/lisp/test-org-element.el (test-org-element/latex-fragment-parser):
  Add test.

In Text mode, and, as a consequence, in Org mode, "'" is not treated
as punctuation, but as word constituent.  The apostrophe isn't caught
by "\s." regexp.

Reported-by: Joe Corneli <holtzermann17@gmail.com>
<http://permalink.gmane.org/gmane.emacs.orgmode/113464>

lisp/org-element.el

@@ -3040,7 +3040,8 @@ Assume point is at the beginning of the LaTeX fragment."
 			 (search-forward "$" nil t 2)
 			 (not (memq (char-before (match-beginning 0))
 				    '(?\s ?\t ?\n ?, ?.)))
-			 (looking-at "\\(\\s.\\|\\s-\\|\\s(\\|\\s)\\|\\s\"\\|$\\)")
+			 (looking-at-p
+			  "\\(\\s.\\|\\s-\\|\\s(\\|\\s)\\|\\s\"\\|'\\|$\\)")
 			 (point)))
 		(pcase (char-after (1+ (point)))
 		  (?\( (search-forward "\\)" nil t))

lisp/org.el

@@ -535,10 +535,10 @@ An entry can be toggled between COMMENT and normal with
 
 (defconst org-latex-regexps
   '(("begin" "^[ \t]*\\(\\\\begin{\\([a-zA-Z0-9\\*]+\\)[^\000]+?\\\\end{\\2}\\)" 1 t)
-    ;; ("$" "\\([ 	(]\\|^\\)\\(\\(\\([$]\\)\\([^ 	\r\n,.$].*?\\(\n.*?\\)\\{0,5\\}[^ 	\r\n,.$]\\)\\4\\)\\)\\([ 	.,?;:'\")]\\|$\\)" 2 nil)
+    ;; ("$" "\\([ \t(]\\|^\\)\\(\\(\\([$]\\)\\([^ \t\n,.$].*?\\(\n.*?\\)\\{0,5\\}[^ \t\n,.$]\\)\\4\\)\\)\\([ \t.,?;:'\")]\\|$\\)" 2 nil)
     ;; \000 in the following regex is needed for org-inside-LaTeX-fragment-p
-    ("$1" "\\([^$]\\|^\\)\\(\\$[^ 	\r\n,;.$]\\$\\)\\(\\s.\\|\\s-\\|\\s(\\|\\s)\\|\\s\"\\|\000\\|$\\)" 2 nil)
-    ("$"  "\\([^$]\\|^\\)\\(\\(\\$\\([^ 	\r\n,;.$][^$\n\r]*?\\(\n[^$\n\r]*?\\)\\{0,2\\}[^ 	\r\n,.$]\\)\\$\\)\\)\\(\\s.\\|\\s-\\|\\s(\\|\\s)\\|\\s\"\\|\000\\|$\\)" 2 nil)
+    ("$1" "\\([^$]\\|^\\)\\(\\$[^ \t\r\n,;.$]\\$\\)\\(\\s.\\|\\s-\\|\\s(\\|\\s)\\|\\s\"\\|\000\\|'\\|$\\)" 2 nil)
+    ("$"  "\\([^$]\\|^\\)\\(\\(\\$\\([^ \t\n,;.$][^$\n\r]*?\\(\n[^$\n\r]*?\\)\\{0,2\\}[^ \t\n,.$]\\)\\$\\)\\)\\(\\s.\\|\\s-\\|\\s(\\|\\s)\\|\\s\"\\|\000\\|'\\|$\\)" 2 nil)
     ("\\(" "\\\\([^\000]*?\\\\)" 0 nil)
     ("\\[" "\\\\\\[[^\000]*?\\\\\\]" 0 nil)
     ("$$" "\\$\\$[^\000]*?\\$\\$" 0 nil))

testing/lisp/test-org-element.el

@@ -1558,6 +1558,10 @@ e^{i\\pi}+1=0
    (eq 'latex-fragment
        (org-test-with-temp-text "$a$ "
 	 (org-element-type (org-element-context)))))
+  (should
+   (eq 'latex-fragment
+       (org-test-with-temp-text "$a$'"
+	 (org-element-type (org-element-context)))))
   (should-not
    (eq 'latex-fragment
        (org-test-with-temp-text "$a$a"