Raise boost baseline version check?

[David Ostrovsky]

Building LO on OpenSUSE 42.2, against the latest available system
boost library (1.54.0), is failing here with:

/home/davido/projects/libo/tools/source/generic/fract.cxx:183:25:
error: ‘boost::integer’ has not been declared
         T gcd1 = boost::integer::gcd(i.numerator(), den);

Looking into the most recent version:

http://www.boost.org/doc/libs/1_64_0/boost/rational.hpp

reveals, that this part of the code is consumed from:

#include <boost/integer/common_factor_rt.hpp> // for
boost::integer::gcd, lcm

On 1.54 the similar line in rational.hpp read:

#include <boost/math/common_factor_rt.hpp>  // for boost::math::gcd,
lcm

So that this diff fixed the problem here:

diff --git a/tools/source/generic/fract.cxx
b/tools/source/generic/fract.cxx
index bc9bef467e86..02fb711c0c84 100644
--- a/tools/source/generic/fract.cxx
+++ b/tools/source/generic/fract.cxx
@@ -180,8 +180,8 @@ namespace
         T den = r.denominator();
 
         // Avoid overflow and preserve normalization
-        T gcd1 = boost::integer::gcd(i.numerator(), den);
-        T gcd2 = boost::integer::gcd(num, i.denominator());
+        T gcd1 = boost::math::gcd(i.numerator(), den);
+        T gcd2 = boost::math::gcd(num, i.denominator());
 
         bool fail = false;
         fail |= o3tl::checked_multiply(i.numerator() / gcd1, num /
gcd2, num);

Unless we want to make the code compile against different boost
versions, should we rather bump the boost version check?

My autogen.input is: [1].

* [1] http://paste.openstack.org/show/608796/