[LyX/master] Ignore QT_SCALE_FACTOR for Qt < 5.6

[Enrico Forestieri]

commit ebd96fadd53fa553b5b09dc21e580df4cf70a2b5
Author: Enrico Forestieri <for...@lyx.org>
Date:   Wed Jan 25 20:00:54 2017 +0100

    Ignore QT_SCALE_FACTOR for Qt < 5.6
    
    This environment variable was introduced in Qt 5.6.0
---
 src/LyX.cpp |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/src/LyX.cpp b/src/LyX.cpp
index bf40298..17094da 100644
--- a/src/LyX.cpp
+++ b/src/LyX.cpp
@@ -312,6 +312,7 @@ int LyX::exec(int & argc, char * argv[])
        // we need to parse for "-dbg" and "-help"
        easyParse(argc, argv);
 
+#if QT_VERSION >= 0x050600
        // Check whether Qt will scale all GUI elements and accordingly
        // set the scale factor so that to avoid blurred images and text
        char const * const scale_factor = getenv("QT_SCALE_FACTOR");
@@ -320,6 +321,7 @@ int LyX::exec(int & argc, char * argv[])
                if (qt_scale_factor < 1.0)
                        qt_scale_factor = 1.0;
        }
+#endif
 
        try {
                init_package(os::utf8_argv(0), cl_system_support, 
cl_user_support);