I just commited revision 8794 to the SVN fixing this bug. Maxima now starts in my system as it should. Notice that in order to see the problem one has to start TeXmacs with a double click, not from the console, nor XCode.
A way to test whether the problem has been fixed is to open a scheme session and execute the following two commands:
(getenv "PATH")
(eval-system "echo $PATH")
If the strings returned are different (in particular if the second call returns something like "/usr/bin:/bin:/usr/sbin:/sbin") then the bug is present.
With r8794 it shouldn't. ;)
Best,