[LyX/master] Fix compiling on platforms lacking setenv

[Enrico Forestieri]

commit b885b80bc0074821c8e98b2d64accd74d5bc08d6
Author: Enrico Forestieri <for...@lyx.org>
Date:   Fri Jul 26 20:48:34 2013 +0200

    Fix compiling on platforms lacking setenv
    
    Using autotools, the availability of putenv is not checked, so
    the macro HAVE_PUTENV is not defined and compiling stops with
    the error "No environment-setting function has been defined."
    Thus, also check for putenv.

diff --git a/configure.ac b/configure.ac
index c5fc54c..4da4881 100644
--- a/configure.ac
+++ b/configure.ac
@@ -173,7 +173,7 @@ fi
 
 LYX_CHECK_DEF(PATH_MAX, limits.h, [int n = PATH_MAX;])
 
-AC_CHECK_FUNCS(chmod close _close fork getpid _getpid lstat mkfifo open _open 
pclose _pclose popen _popen readlink setenv strerror unsetenv)
+AC_CHECK_FUNCS(chmod close _close fork getpid _getpid lstat mkfifo open _open 
pclose _pclose popen _popen readlink putenv setenv strerror unsetenv)
 # Check the form of mkdir()
 AC_FUNC_MKDIR
 AC_FUNC_SELECT_ARGTYPES