Maintain ordering of header

[ronlevine]

Description

Implements #847.

Checklist

• Code compiles correctly
• New tests covering changes and new functionality
• All tests passing
• Extended the README / documentation, if necessary
• Is not backward compatible (breaks binary or source compatibility)

[ronlevine]

@lbergelson Please review.

[codecov-io]

Codecov Report

Merging #848 into master will increase coverage by 0.006%.
The diff coverage is 100%.

@@              Coverage Diff               @@
##             master      #848       +/-   ##
==============================================
+ Coverage     64.86%   64.866%   +0.006%     
- Complexity     7195      7197        +2     
==============================================
  Files           527       527               
  Lines         31781     31781               
  Branches       5424      5424               
==============================================
+ Hits          20613     20615        +2     
  Misses         9020      9020               
+ Partials       2148      2146        -2

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/htsjdk/variant/vcf/VCFUtils.java	24.706% <100%> (ø)	6 <6> (ø)	⬇️
...dk/samtools/seekablestream/SeekableHTTPStream.java	54.545% <0%> (-1.515%)	9% <0%> (-1%)
...main/java/htsjdk/samtools/SAMRecordSetBuilder.java	89.113% <0%> (+0.806%)	64% <0%> (+2%)	⬆️
...a/htsjdk/samtools/cram/encoding/rans/Decoding.java	85.714% <0%> (+3.571%)	12% <0%> (+1%)	⬆️

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[ronlevine]

@yfarjoun Could you take a look? Louis will be on vacation.

[yfarjoun]

looks good @ronlevine. Could you split into two commits, test and code change and push them separately (so that travis will initiate a build on both commits)? I'd like to see that the old code breaks the tests.

[ronlevine]

@yfarjoun Done. Take a look at the last 2 travis runs.

[yfarjoun]

Thank @ronlevine. 👍