[LyX/2.2.x] We can now use the cached information instead of tracing the graph.

[Richard Heck]

commit 348c95d1bfaa02f600787e386e33b628af7f4b59
Author: Richard Heck <rgh...@lyx.org>
Date:   Thu Oct 20 22:52:54 2016 -0400

    We can now use the cached information instead of tracing the graph.
    
    (cherry picked from commit 7c9e9b4c90fade3be8623a9fc1a509e06872a9cd)
---
 src/BufferParams.cpp |   10 ++++++----
 1 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/BufferParams.cpp b/src/BufferParams.cpp
index e409dff..8af927a 100644
--- a/src/BufferParams.cpp
+++ b/src/BufferParams.cpp
@@ -2403,11 +2403,13 @@ string BufferParams::bufferFormat() const
 
 bool BufferParams::isExportable(string const & format) const
 {
-       vector<string> backs = backends();
-       for (vector<string>::const_iterator it = backs.begin();
-            it != backs.end(); ++it)
-               if (theConverters().isReachable(*it, format))
+       FormatList const & formats = exportableFormats(false);
+       FormatList::const_iterator fit = formats.begin();
+       FormatList::const_iterator end = formats.end();
+       for (; fit != end ; ++fit) {
+               if ((*fit)->name() == format)
                        return true;
+       }
        return false;
 }