Change 'ensure-directories-exist' to look for 'mkdir' in $PATH, not in /bin.

--- maxima-5.36.1/lisp-utils/defsystem.lisp.orig	2014-11-22 16:21:30.000000000 -0500
+++ maxima-5.36.1/lisp-utils/defsystem.lisp	2015-05-25 21:53:31.223648483 -0400
@@ -4627,7 +4627,7 @@
         (cmd (if (member :win32 *features*)
                  (format nil "mkdir \"~a\""
                          (coerce (subst #\\ #\/ (coerce (namestring dir) 'list)) 'string))
-                 (format nil "/bin/mkdir -p ~S" (namestring dir)))))
+                 (format nil "mkdir -p ~S" (namestring dir)))))
    (unless (directory dir)
      (lisp:system cmd))
    ;; The second return value is supposed to be T if directories were
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<div class='path'>path: <a href='/guix/log/?id=29e83e1c70a0738e2e4c8e55ab76a701c9fac12f'>root</a>/<a href='/guix/log/build-aux?id=29e83e1c70a0738e2e4c8e55ab76a701c9fac12f'>build-aux</a>/<a href='/guix/log/build-aux/check-available-binaries.scm?id=29e83e1c70a0738e2e4c8e55ab76a701c9fac12f'>check-available-binaries.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/build-aux/check-available-binaries.scm?id=29e83e1c70a0738e2e4c8e55ab76a701c9fac12f&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2016-04-27 15:00:49 +0200'>2016-04-27</span></td><td><a href='/guix/commit/build-aux/check-available-binaries.scm?id=f1ebeee131d7b73c26689741fa48f55a5dd5b1de'>build: 'make assert-binaries-available' shows the list of systems.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/check-available-binaries.scm: Display %HYDRA-SUPPORTED-SYSTEMS.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2016-03-03 23:54:36 +0100'>2016-03-03</span></td><td><a href='/guix/commit/build-aux/check-available-binaries.scm?id=5c7e1a32709365949ebc952109621bc770d44664'>build: Use (guix grafts) as needed.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is a followup to 7adf9b8.

* build-aux/check-final-inputs-self-contained.scm: Use (guix grafts).
* build-aux/check-available-binaries.scm: Likewise.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-07-21 22:28:20 +0200'>2015-07-21</span></td><td><a href='/guix/commit/build-aux/check-available-binaries.scm?id=e348eaaf318646e259a5e6803133ad5b296febc1'>check-available-binaries: Use 'substitutable-paths'.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/check-available-binaries.scm: Rewrite to use 'substitutable-paths'
  instead of 'substitution-oracle'.  The latter does more than we need, and it
  no longer check the substitutability of valid items, which is not what we
  want.  Use 'lset-difference' instead of iterating over the items.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-05-01 17:38:09 +0200'>2015-05-01</span></td><td><a href='/guix/commit/build-aux/check-available-binaries.scm?id=78bed82d193d73488f18d76165aa3f809122311f'>check-available-binaries: Use %HYDRA-SUPPORTED-SYSTEMS.</a><span class='msg-avail'>...<span class='msg-tooltip'>* build-aux/check-available-binaries.scm: Use %HYDRA-SUPPORTED-SYSTEMS
  instead of %SUPPORTED-SYSTEMS.
</span></span></td><td>Ludovic Courtès</td></tr>