Windows: Don't test ispath on deleted file or dir

These are failing with "stat: operation not permitted (EPERM)". There may still be
file handles open so the unlinked file and removed directory cannot be stat-ed.
Added mark/unmark/reset/ismarked to IOStream, IOBuffer, and AsyncStream
Also added show() for IOBuffer.

* Define mark, reset, unmark, ismarked for IO only.
  This is slightly sketchy, as it assumes that IO.mark exists, but
  is perhaps better than duplicating the code for all subtypes.
Fix rare and unlikely early free

During bootsrap, some code called the generic "map"
triggering compilation of the inference code in
jl_apply_generic -> jl_mt_assoc_by_type ->
cache_method. This particular map method gets
overwritten in the process and by the time
jl_apply_generic gets its function pointer back, it
is not present in the method table anymore.
Then, in jl_trampoline, compilation allocates some
managed memory, sometimes triggering GC, thus
sometimes freeing the function object before it is
called.
fix missing root on module allocation
Remove UNDOCUMENTED.rst from docs
Add lyap() and sylvester().
Test for lyap() and sylvester()
and taking some tests out of the inner loop in linalg1.jl
Fix: Scale is real
Doc for lyap() and sylvester().
Avoid explicit transposes
Names the actual script that gets run by Pkg.build
reverts mistaken grammatical change
cast to unsigned char for each use of isspace
readcsv can read true and false strings as Bool.
fixes #7463
Use chksquare in trsyl!
Merge pull request #7414 from JuliaLang/cjh/del-undoc

Remove UNDOCUMENTED.rst from docs
Dimension check in gemv! plus tests of same
Merge pull request #7471 from JuliaLang/db/gemv

Dimension check in gemv! plus tests of same
Merge pull request #6144 from tkelman/patch-2

Windows test failures in file.jl: "stat: operation not permitted (EPERM)"
add direct support for more integer types in iround. fixes #7441

also add more Float16 -> Integer conversions