Fixes a fuzz issue where dictionary_round_trip failed because the compressor was generating corrupt files thanks to zero weights in the table.

* Only setting loaded dict huf table to valid on non-zero

* Adding hasNoZeroWeights test to fse tables

* Forbiding nbBits != 0 when weight == 0

* Reverting the last commit

* Setting table log to 0 when weight == 0

* Small (invalid) zero weight dict test

* Small (valid) zero weight dict test

* Initializing repeatMode vars to check before zero check

* Removing FSE changes to seperate pr

* Reverting accidentally changed file

* Negating bool, using unsigned, optimization nit

fix #1904

* Optimize `ZSTD_decodeSequence()`
* Optimize Huffman decoding
* Optimize `ZSTD_decompressSequences()`
* Delete `ZSTD_decodeSequenceLong()`

protecting "/dev/null" from having its permissions changed.

also : minor : improved consistency of util.h API

/dev/null permissions were modified when using sudo rights.
This fixes this bug during decompression.

More importantly, this patch  adds a test, triggered in TravisCI,
ensuring unaltered /dev/null permissions.

many tests used to be run on Trusty platform,
they are now run on _current_ platform,
and now many test titles are incorrect.
Fixed.

WIP: Fix typo in util.c

Fix null pointer addition

[cmake][tests] Add zstreamtest executable

Update .gitignore

Easy: Update Comment on `ZSTD_initDStream()`

Fixing hashLog error 2^26=64Mib

Fix Appveyor failure

There must be mtim*e*

Optimized loop bounds to allow the compiler to unroll the loop.

RLE test and re-enable RLE in main compression loop

shared library: rename import library with .dll.a extension

mort of open source project are using this extension for the import library.
The Win32 linker is supporting this extension, see
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/4/html/Using_ld_the_GNU_Linker/win32.html
section "direct linking to a dll"

This has no measurable impact on large files but improves small file
decompression by ~1-2% for 10kB, benchmarked with:

head -c 10000 silesia.tar > /tmp/test
make CC=/usr/local/bin/clang-9 BUILD_STATIC=1 && ./lzbench -ezstd -t1,5 /tmp/test

Superblocks rebased for merge

Method to get dictionary header size

Specs. clarifications for Block_Maximum_Size

as a follow up of #1882

Change c90 to c89