admin.el: respect environment settings for makeinfo etc

* admin/admin.el (manual-makeinfo, manual-texi2pdf, manual-texi2dvi):
New variables.
(manual-html-mono, manual-html-node, manual-pdf, manual-ps): Use them.

admin/admin.el

@@ -352,13 +352,22 @@ Optional argument TYPE is type of output (nil means all)."
     (manual-html-mono texi (expand-file-name (concat name ".html")
 					     html-mono-dir))))
 
+(defvar manual-makeinfo (or (getenv "MAKEINFO") "makeinfo")
+  "The `makeinfo' program to use.")
+
+(defvar manual-texi2pdf (or (getenv "TEXI2PDF") "texi2pdf")
+  "The `texi2pdf' program to use.")
+
+(defvar manual-texi2dvi (or (getenv "TEXI2DVI") "texi2dvi")
+  "The `texi2dvi' program to use.")
+
 (defun manual-html-mono (texi-file dest)
   "Run Makeinfo on TEXI-FILE, emitting mono HTML output to DEST.
 This function also edits the HTML files so that they validate as
 HTML 4.01 Transitional, and pulls in the gnu.org stylesheet using
 the @import directive."
   (make-directory (or (file-name-directory dest) ".") t)
-  (call-process "makeinfo" nil nil nil
+  (call-process manual-makeinfo nil nil nil
 		"-D" "WWW_GNU_ORG"
 		"-I" (expand-file-name "../emacs"
 				       (file-name-directory texi-file))
@@ -386,7 +395,7 @@ the @import directive."
   (unless (file-exists-p texi-file)
     (user-error "Manual file %s not found" texi-file))
   (make-directory dir t)
-  (call-process "makeinfo" nil nil nil
+  (call-process manual-makeinfo nil nil nil
 		"-D" "WWW_GNU_ORG"
 		"-I" (expand-file-name "../emacs"
 				       (file-name-directory texi-file))
@@ -425,7 +434,7 @@ the @import directive."
   "Run texi2pdf on TEXI-FILE, emitting PDF output to DEST."
   (make-directory (or (file-name-directory dest) ".") t)
   (let ((default-directory (file-name-directory texi-file)))
-    (call-process "texi2pdf" nil nil nil
+    (call-process manual-texi2pdf nil nil nil
 		  "-I" "../emacs" "-I" "../misc"
 		  texi-file "-o" dest)))
 
@@ -435,7 +444,7 @@ the @import directive."
   (let ((dvi-dest (concat (file-name-sans-extension dest) ".dvi"))
 	(default-directory (file-name-directory texi-file)))
     ;; FIXME: Use `texi2dvi --ps'?  --xfq
-    (call-process "texi2dvi" nil nil nil
+    (call-process manual-texi2dvi nil nil nil
 		  "-I" "../emacs" "-I" "../misc"
 		  texi-file "-o" dvi-dest)
     (call-process "dvips" nil nil nil dvi-dest "-o" dest)