Add boost chrono lib for windows builds (required for boost 1.50)

bitcoin-qt.pro

@@ -359,6 +359,7 @@ LIBS += -lssl -lcrypto -ldb_cxx$$BDB_LIB_SUFFIX
 # -lgdi32 has to happen after -lcrypto (see  #681)
 windows:LIBS += -lole32 -luuid -lgdi32
 LIBS += -lboost_system$$BOOST_LIB_SUFFIX -lboost_filesystem$$BOOST_LIB_SUFFIX -lboost_program_options$$BOOST_LIB_SUFFIX -lboost_thread$$BOOST_THREAD_LIB_SUFFIX
+windows:LIBS += -lboost_chrono$$BOOST_LIB_SUFFIX
 
 contains(RELEASE, 1) {
     !windows:!macx {

src/makefile.linux-mingw

@@ -25,6 +25,7 @@ LIBS= \
  -l boost_filesystem-mt-s \
  -l boost_program_options-mt-s \
  -l boost_thread_win32-mt-s \
+ -l boost_chrono-mt-s \
  -l db_cxx \
  -l ssl \
  -l crypto

src/makefile.mingw

@@ -20,6 +20,7 @@ LIBS= \
  -l boost_filesystem-mgw45-mt-s-1_50 \
  -l boost_program_options-mgw45-mt-s-1_50 \
  -l boost_thread-mgw45-mt-s-1_50 \
+ -l boost_chrono-mgw45-mt-s-1_50 \
  -l db_cxx \
  -l ssl \
  -l crypto