correct links (mdbook seems to want them relative to the book root)

Author: nikomatsakis

src/how-to-build-and-run.md

@@ -132,6 +132,6 @@ Here are a few other useful x.py commands. We'll cover some of them in detail in
   - `./x.py clean` – clean up the build directory (`rm -rf build` works too, but then you have to rebuild LLVM)
   - `./x.py build --stage 1` – builds everything using the stage 1 compiler, not just up to libstd
   - `./x.py build` – builds the stage2 compiler
-- Running tests (see the section [running tests](./running-tests.html) for more details):
+- Running tests (see the [section on running tests](./tests/running.html) for more details):
   - `./x.py test --stage 1 src/libstd` – runs the `#[test]` tests from libstd
   - `./x.py test --stage 1 src/test/run-pass` – runs the `run-pass` test suite

src/tests/adding.md

@@ -9,7 +9,7 @@ To add a new test, the first thing you generally do is to create a
 file, typically a Rust source file. Test files have a particular
 structure:
 
-- They always begin with the [copyright notice](../conventions.html#copyright);
+- They always begin with the [copyright notice](./conventions.html#copyright);
 - then they should have some kind of
   [comment explaining what the test is about](#explanatory_comment);
 - next, they can have one or more [header commands](#header_commands), which are special

src/tests/intro.md

@@ -4,8 +4,8 @@ The compiler has an extensive testing framework, masterminded by the
 compiletest tool (sources in the [`src/tools/compiletest`]). This
 section gives a brief overview of how the testing framework is setup,
 and then gets into some of the details on
-[how to run tests](running.html) as well as
-[how to add new tests](adding.html).
+[how to run tests](./tests/running.html#ui) as well as
+[how to add new tests](./tests/adding.html).
 
 [`src/tools/compiletest`]: https://github.com/rust-lang/rust/tree/master/src/tools/compiletest
 
@@ -23,7 +23,7 @@ Here is a brief summary of the test suites as of this writing and what
 they mean. In some cases, the test suites are linked to parts of the manual
 that give more details.
 
-- [`ui`](adding.html#) -- tests that check the exact stdout/stderr from compilation
+- [`ui`](./tests/adding.html#ui) -- tests that check the exact stdout/stderr from compilation
   and/or running the test
 - `run-pass` -- tests that are expected to compile and execute successfully (no panics)
   - `run-pass-valgrind` -- tests that ought to run with valrind

src/tests/running.md

@@ -18,7 +18,7 @@ think is done, but rarely otherwise. -nmatsakis)
 When you run the full suite of tests via `./x.py test`, the first
 thing that executes is a "tidy suite" that checks for long lines and
 other formatting conventions. There is more information in the
-[section on coding conventions](../conventions.html#formatting).
+[section on coding conventions](./conventions.html#formatting).
 
 ## Running a subset of the test suites