headers/kernel: Move B_WAIT_TILL_LOADED to a syscall header.

It is only used as an argument to _kern_load_image directly, not to
any of the load_image functions in image.h, so it belongs in a syscall-
specific header like other such constants.

No functional change intended.

Implement support for a SYS:ENV attribute on executable

__flatten_process_args() does now have the executable path as an
additional (optional) parameter. If specified, the function will read
the file's SYS:ENV attribute (if set) and use its value to modified the
environment it is preparing for the new process. Currently supported
attribute values are strings consisting of "<var>=<value>" substrings
separated by "\0" (backslash zero), with '\' being used as an escape
character. The environment will be altered to contain the specified
"<var>=<value>" elements, replacing a preexisting <var> element (if
any).

A possible use case would be setting a SYS:ENV attribute with value
"DISABLE_ASLR=1" on an executable that needs ASLR disabled.

Added a few classes to the debug kit:
* BDebugMessageHandler: Interface with hooks for handling of debug messages.
* BDebugContext: Essentially a C++ wrapper for struct debug_context, with
handy methods for controlling a debugged team.
* BTeamDebugger: Proxy for a debugged team. Derived from BDebugContext.
* BDebugLooper: Wraps a main debug message loop. Any number of BTeamDebuggers
can be added and associated with BDebugMessageHandlers.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@35953 a95241bf-73f2-0310-859d-f6bbb57e9c96

Implement support for a SYS:ENV attribute on executable

__flatten_process_args() does now have the executable path as an
additional (optional) parameter. If specified, the function will read
the file's SYS:ENV attribute (if set) and use its value to modified the
environment it is preparing for the new process. Currently supported
attribute values are strings consisting of "<var>=<value>" substrings
separated by "\0" (backslash zero), with '\' being used as an escape
character. The environment will be altered to contain the specified
"<var>=<value>" elements, replacing a preexisting <var> element (if
any).

A possible use case would be setting a SYS:ENV attribute with value
"DISABLE_ASLR=1" on an executable that needs ASLR disabled.

Added a few classes to the debug kit:
* BDebugMessageHandler: Interface with hooks for handling of debug messages.
* BDebugContext: Essentially a C++ wrapper for struct debug_context, with
handy methods for controlling a debugged team.
* BTeamDebugger: Proxy for a debugged team. Derived from BDebugContext.
* BDebugLooper: Wraps a main debug message loop. Any number of BTeamDebuggers
can be added and associated with BDebugMessageHandlers.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@35953 a95241bf-73f2-0310-859d-f6bbb57e9c96