Also search through /usr/local/lib in yabridgectl

For automatic path detection. It's still not recommended to install
yabridge there, but if you know what you're doing then this would at
least be a good default to have.

CHANGELOG.md

@@ -12,6 +12,9 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 - Resolve relative paths when adding plugin directories or when changing
   settings.
+- Also search `/usr/local/lib` for `libyabridge.so` when no manual path has been
+  specified. Note that manually copying yabridge's files to `/usr` is still not
+  recommended.
 
 ## [1.6.0] - 2020-09-17
 

tools/yabridgectl/src/config.rs

@@ -176,10 +176,14 @@ impl Config {
                 }
             }
             None => {
-                // Search in the two common installation locations if no path was set explicitely
+                // Search in the two common installation locations if no path was set explicitely.
+                // We'll also search through `/usr/local/lib` just in case but since we advocate
+                // against isntalling yabridge there we won't list this path in the error message
+                // when `libyabridge.so` can't be found.
                 let system_path = Path::new("/usr/lib");
+                let system_path_alt = Path::new("/usr/local/lib");
                 let user_path = yabridge_directories()?.get_data_home();
-                for directory in &[system_path, &user_path] {
+                for directory in &[system_path, system_path_alt, &user_path] {
                     let candidate = directory.join(LIBYABRIDGE_NAME);
                     if candidate.exists() {
                         return Ok(candidate);