Fixed incorrect usage of 'Borrowing'.
Fix missing parenthesis in a previous substitution '$(PREFIX_ROOT)' to  '$(CFG_MANDIR' on 1c4a348b072a
auto merge of #10193 : osaut/rust/Fix_install, r=huonw

Fix missing parentheses coming from a previous substitution '$(PREFIX_ROOT)' to  '$(CFG_MANDIR' on 1c4a348b072a
auto merge of #10167 : briantdawn/rust/master, r=cmr

To keep consistency with the word "borrowing" I suppose an alternate way to write this could be "Having an object borrow an immutable pointer freezes it and prevents mutation".
Implement a concat!() format extension

This extension can be used to concatenate string literals at compile time. C has
this useful ability when placing string literals lexically next to one another,
but this needs to be handled at the syntax extension level to recursively expand
macros.

The major use case for this is something like:

    macro_rules! mylog( ($fmt:expr $($arg:tt)*) => {
        error2!(concat!(file!(), ":", line!(), " - ", $fmt) $($arg)*);
    })

Where the mylog macro will automatically prepend the filename/line number to the
beginning of every log message.
Fix fallback configuration flags
auto merge of #10206 : brson/rust/configure, r=brson
auto merge of #9740 : alexcrichton/rust/concat, r=cmr

This extension can be used to concatenate string literals at compile time. C has
this useful ability when placing string literals lexically next to one another,
but this needs to be handled at the syntax extension level to recursively expand
macros.

The major use case for this is something like:

    macro_rules! mylog( ($fmt:expr $($arg:tt)*) => {
        error2!(concat!(file!(), ":", line!(), " - ", $fmt) $($arg)*);
    })

Where the mylog macro will automatically prepend the filename/line number to the
beginning of every log message.