Avoid conversion to Array to stream vectors to error messages.

Thanks to Johannes Göttker-Schnetmann for the heads-up.

git-svn-id: svn://svn.code.sf.net/p/quantlib/code/trunk/QuantLib@18494 8618b1d8-e22c-0410-b026-96a5dba3e089
Avoided warnings in VC++ when compiling in x64 configuration.

Thanks to Johannes Göttker-Schnetmann.

git-svn-id: svn://svn.code.sf.net/p/quantlib/code/trunk/QuantLib@18495 8618b1d8-e22c-0410-b026-96a5dba3e089