Revert to c++14 due to pqxx compilation issues in c++17 on older OSes

Ubuntu18, Centos7.6 have pqxx that won't compile in c++17 mode.
This sounds like a bad dependency/include issue, though, as p1transform
shouldn't need to know that pqxx is involved in IRDB management.

SConstruct

@@ -43,7 +43,7 @@ env.Replace(debug=ARGUMENTS.get("debug",0))   # build in debug mode?
 #
 # Required:  need these flag to appropriately include/link IRDB files.
 #
-env.Append(CXXFLAGS=" -std=c++17 ")	# enable c++17
+env.Append(CXXFLAGS=" -std=c++14 ")	# enable c++17
 env.Append(LINKFLAGS=" -Wl,-unresolved-symbols=ignore-in-shared-libs ") # irdb libs may have symbols that resolve OK at runtime, but not linktime.