Replaced Linux syscall macros by libc macros.

User-space programs should use the SYS_*form, as documented in
syscall(2). That also adds compatibility to non-Linux systems.

Fixed indentation.

Some lines (incorrectly) had an indentation of 3 or 5, or 7 or 9,
or 11 or 13, or 15 or 17 spaces instead of 4, 8, 12, or 16. Fix them.

Found with:

$ find src -type f | xargs g

Fixed indentation.

Some lines (incorrectly) had an indentation of 3 or 5, or 7 or 9,
or 11 or 13, or 15 or 17 spaces instead of 4, 8, 12, or 16. Fix them.

Found with:

$ find src -type f | xargs grep -n '^ [^ ]';
$ find src -type f | xargs grep -n '^ [^ *]';
$ find src -type f | xargs grep -n '^ [^ ]';
$ find src -type f | xargs grep -n '^ [^ *]';
$ find src -type f | xargs grep -n '^ [^ +]';
$ find src -type f | xargs grep -n '^ [^ *+]';
$ find src -type f | xargs grep -n '^ [^ +]';
$ find src -type f | xargs grep -n '^ [^ *+]';

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Isolation: allowed the use of credentials with unpriv userns.

The setuid/setgid syscalls requires root capabilities but if the kernel
supports unprivileged user namespace then the child process has

Isolation: allowed the use of credentials with unpriv userns.

The setuid/setgid syscalls requires root capabilities but if the kernel
supports unprivileged user namespace then the child process has the full
set of capabilities in the new namespace, then we can allow setting "user"
and "group" in such cases (this is a common security use case).

Tests were added to ensure user gets meaningful error messages for
uid/gid mapping misconfigurations.

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Closing leaking file descriptor.

Found by Coverity (CID 349484).

Initial applications isolation support using Linux namespaces.