Less stringent sanity check in vcf-convert

git-svn-id: https://svn.code.sf.net/p/vcftools/code@871 19d466ce-640d-45be-954f-fad4d9839663
vcf-convert: Case insensitive sanity check

git-svn-id: https://svn.code.sf.net/p/vcftools/code@872 19d466ce-640d-45be-954f-fad4d9839663
Merge remote-tracking branch 'upstream'