disable file_converter if boost is not found.

12 jobs from fix_boost in 3 minutes and 43 seconds
Status Job ID Name Coverage
  Test
passed #21627
VS2013
VS2013-32-bit

00:00:51

passed #21626
VS2013
VS2013-64-bit

00:00:53

passed #21625
VS2015
VS2015-32-bit

00:01:01

passed #21624
VS2015
VS2015-64-bit

00:01:17

passed #21618
Linux
clang-c++11

00:02:23

passed #21620
Linux
clang-c++98

00:01:55

passed #21623
Linux
cppcheck

00:01:49

passed #21628
Linux
doc

00:00:16

passed #21617
Linux
gcc-c++11

00:03:42

passed #21619
Linux
gcc-c++98

00:02:51

passed #21621
Apple
macos-c++11

00:01:24

passed #21622
Apple
macos-c++98

00:01:19