add integration test for vcf-report
bugfix for v1.6: vcf-report crashes on empty alt field
backport of bugfix from master:

memory leak in vcf-report
warn instead of fail on duplicate (identical) INFO/FORMAT header fields
indel normalization code code cleanup
add -N option to vcf-merge to normalize indels
fix alt renumbering in normalize indels

vcf-normalize-indels does alt allele deduplication, but was failing to
correctly update GT fields when it renumbers alts
add --exact-pos option to joinx vcf-merge
make ref-stats command case insensitive
update build instructions in readme.
remove hard coded values of FindBoost parameters
update build-common
relax boost requirement from 1.51 to 1.48
use gtest from build-common/vendor instead of system
add vcf2raw command to strip vcf entries down to raw alleles
don't try to normalize substitutions
update build-common submodule
update unit tests to build one executable per library
set vcf info fields after alt/gt data when merging
update build-common submodule