docs: fix upper bound on number of consumed cores

docs: xref doesn't render in title

https://hydra.nixos.org/build/105428308

docs: correct default location of log directory

Update nix eval --help msg to not include deprecated command

Fix progress bar when nix-prefetch-url is piped.

The intent of the code was that if the window size cannot be determined,
it would be treated as having the maximum possible size. Because of a
missing assignment, it was actually treated as having a width of 0.

The reason the width could not be determined was because it was obtained
from stdout, not stderr, even though the printing was done to stderr.

This commit addresses both issues.

The `post-build-hook` text currently appears in the index, but not on the actual title line of the section, this follows the pattern used in a previous section to get a reference into a title.

include netinet/in.h in src/nix/main.cc

Fixes #3186

travis: enable linux builds

Also disable email to not notify the whole NixOS community about build failures

Minor updates to inline comments

minor: fix mismatch of struct/class forward decl of 'Source'

Add missing docstring on InstallableCommand. Also, some of these were wrapped
when they're right next to a line longer than the unwrapped line, so we can just
unwrap them to save vertical space.

Fixes the following warning and the indicate potential issue:

src/libstore/worker-protocol.hh:66:1: warning: class 'Source' was previously declared as a struct; this is valid, but may result in linker errors
under the Microsoft C++ ABI [-Wmismatched-tags]

(cherry picked from commit 6e1bb04870b1b723282d32182af286646f13bf3c)

Also drop multithread-unfriendly hacks like doing a temporary
chmod/umask.

This is an alternative to the IN_NIX_SHELL environment variable,
allowing the expression to adapt itself to nix-shell without
triggering those adaptations when used as a dependency of another
shell.

Closes #3147

https://hydra.nixos.org/build/104119659

Remove superfluous IAM action for S3 cache

Document import <path> syntax

`s3:ListObjects` isn't a real IAM action, but _is_ the name of an S3 API method. `s3:ListBucket` is the relevant action for that method.

https://docs.aws.amazon.com/IAM/latest/UserGuide/list_amazons3.html