[LyX/master] Fix missing include for file i/o prototypes after header cleanup in change 489dca71cd99bbc78780fa40311a2eb042c0320e

[Stephan Witt]

commit df73cade2bdbf272f5228ec895d97c21a20242d5
Author: Stephan Witt <sw...@lyx.org>
Date:   Mon Jul 4 10:30:19 2016 +0200

    Fix missing include for file i/o prototypes after header cleanup in change 
489dca71cd99bbc78780fa40311a2eb042c0320e
---
 src/ServerSocket.cpp |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/src/ServerSocket.cpp b/src/ServerSocket.cpp
index ece3549..fd903ce 100644
--- a/src/ServerSocket.cpp
+++ b/src/ServerSocket.cpp
@@ -39,6 +39,10 @@
 # include <io.h>
 #endif
 
+#ifdef HAVE_UNISTD_H
+# include <unistd.h>
+#endif
+
 using namespace std;
 using namespace lyx::support;