[LyX/master] Avoids const_cast in configure_command by using mutable

[Richard Heck]

commit 73405549cb122d30dfdba13414660a3427eb0db2
Author: Benjamin Piwowarski <bpiwo...@lyx.org>
Date:   Fri Mar 21 18:38:09 2014 +0100

    Avoids const_cast in configure_command by using mutable

diff --git a/src/support/Package.cpp b/src/support/Package.cpp
index f5ee5d5..b4b0e14 100644
--- a/src/support/Package.cpp
+++ b/src/support/Package.cpp
@@ -154,9 +154,8 @@ Package::Package(string const & command_line_arg0,
 std::string const & Package::configure_command() const
 {
        if (configure_command_.empty()) {
-               std::string &command = 
const_cast<std::string&>(configure_command_);
                FileName const 
configure_script(addName(system_support().absFileName(), "configure.py"));
-               command = os::python() + ' ' +
+               configure_command_ = os::python() + ' ' +
                        quoteName(configure_script.toFilesystemEncoding()) +
                        with_version_suffix() + " --binary-dir=" +
                        
quoteName(FileName(binary_dir().absFileName()).toFilesystemEncoding());