Fix case sensitivity issue in VariantHeaderBuilder that was preventing shared/individual field types from getting set

Quick fix needed by Joel
Merge pull request #298 from broadinstitute/dr_variant_header_builder_case_sensitivity_bug

Fix case sensitivity issue in VariantHeaderBuilder that was preventing shared/individual field types from getting set
Merge variant headers
- Merge bcf_hdr_t with merge_variant_headers()
- Merge VariantHeader with VariantHeaderBuilder::merge()

Add VariantHeader equality operators
Merge pull request #293 from broadinstitute/jt_variant_header_merge

Merge Variant Headers
Travis: run tests in release mode in master only

create a new *production* mode to eliminate the -finline-functions that
is no longer supported by clang 3.5

also create a global fixture for initialization of global variables in
the variant reader test.

closes #290
Merge pull request #291 from broadinstitute/mc_relase_mode_testing

Travis: run tests in release mode in master only
Fix handling of vector end values by Genotype::operator[]

Vector end values were not passing through to the caller
when accessing alleles via operator[] in the Genotype class.
Merge pull request #302 from broadinstitute/dr_fix_genotype_handling_of_vector_end

Fix handling of vector end values by Genotype::operator[]
Read group class