Changed std::fabs to std::abs in AssertionUtilities.h to avoid compile...

Changed std::fabs to std::abs in AssertionUtilities.h to avoid compile ambiguity error on Windows with TestReferenceCustomHbondForce

tests/AssertionUtilities.h

@@ -58,10 +58,10 @@ void throwException(const char* file, int line, const std::string& details) {
 
 #define ASSERT_EQUAL(expected, found) {if (!((expected) == (found))) {std::stringstream details; details << "Expected "<<(expected)<<", found "<<(found); throwException(__FILE__, __LINE__, details.str());}};
 
-#define ASSERT_EQUAL_TOL(expected, found, tol) {double _scale_ = std::fabs(expected) > 1.0 ? std::fabs(expected) : 1.0; if (!(std::fabs((expected)-(found))/_scale_ <= (tol))) {std::stringstream details; details << "Expected "<<(expected)<<", found "<<(found); throwException(__FILE__, __LINE__, details.str());}};
+#define ASSERT_EQUAL_TOL(expected, found, tol) {double _scale_ = std::abs(expected) > 1.0 ? std::abs(expected) : 1.0; if (!(std::abs((expected)-(found))/_scale_ <= (tol))) {std::stringstream details; details << "Expected "<<(expected)<<", found "<<(found); throwException(__FILE__, __LINE__, details.str());}};
 
 #define ASSERT_EQUAL_VEC(expected, found, tol) {ASSERT_EQUAL_TOL((expected)[0], (found)[0], (tol)); ASSERT_EQUAL_TOL((expected)[1], (found)[1], (tol)); ASSERT_EQUAL_TOL((expected)[2], (found)[2], (tol));};
 
-#define ASSERT_USUALLY_EQUAL_TOL(expected, found, tol) {double _scale_ = std::fabs(expected) > 1.0 ? std::fabs(expected) : 1.0; if (!(std::fabs((expected)-(found))/_scale_ <= (tol))) {std::stringstream details; details << "Expected "<<(expected)<<", found "<<(found)<<" (This test is stochastic and may occasionally fail)"; throwException(__FILE__, __LINE__, details.str());}};
+#define ASSERT_USUALLY_EQUAL_TOL(expected, found, tol) {double _scale_ = std::abs(expected) > 1.0 ? std::abs(expected) : 1.0; if (!(std::abs((expected)-(found))/_scale_ <= (tol))) {std::stringstream details; details << "Expected "<<(expected)<<", found "<<(found)<<" (This test is stochastic and may occasionally fail)"; throwException(__FILE__, __LINE__, details.str());}};
 
 #endif /*OPENMM_ASSERTIONUTILITIES_H_*/