The crypt(3) function is not available in Android, so remove support
in ext for now.

diff -u -r ../picoLisp/src/ext.c ./src/ext.c
--- ../picoLisp/src/ext.c	2015-11-27 02:25:22.000000000 -0500
+++ ./src/ext.c	2016-02-08 06:19:58.405969024 -0500
@@ -250,6 +250,7 @@
    return T;
 }
 
+#ifndef __ANDROID__
 /*** Password hashing ***/
 // (ext:Crypt 'key 'salt) -> str
 any Crypt(any x) {
@@ -269,3 +270,4 @@
       }
    }
 }
+#endif